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An epic adventure of monkeys vs. Bloons...
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Before the rise of man brought the great rivalry between Pirate and Ninja, there was another natural feud between two animal species: Monkeys... and B[al]loons. No one knows how or why this epic war began, but both sides fight endlessly with ever greater wartime developments vying for domination of the world. All of the preceding is included absolutely nowhere in the game's design, and is merely a flavorful fantasy explaining why players seem to care so much about using monkeys to pop balloons.

Bloons Tower Defense (or BTD as it's abbreviated) is an ongoing Tower Defense series by Ninja Kiwi where monkeys (and other weapons) are used to pop a seemingly endless line of overly determined balloons of varying shapes, sizes, and speed. Though starting out with a simplified design palette, later editions of the game have evolved to include a great deal of complexity in both art and gameplay mechanics.

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This game was a spinoff of the lesser known Bloons (a series of aim-and-power-meter puzzle games with many player-designed maps). However, it became so much more popular that this series got its own spinoff, Bloons Super Monkey. This takes the form of a top-down aerial shooter starring the titular monkey from the BTD series, inspired by Raiden X. The basic goal is to pop a set number of bloons in each level, upgrading along the way to beat levels with increasingly strong Bloon formations. It even got its own sequel and a mobile remake thereof!

Three other spinoffs of this series exist:

  • Bloons Monkey City, a tower-defense city-simulator combo with has elements of Facebook games where Player Versus Player is possible.
  • Bloons TD Battles where PvP is the primary focus; the primary modes are Assault and Defensive. Assault has you and your opponent try to defeat each other by sending bloons, in addition to AI-spawned bloonsnote . Defensive instead focuses on surviving the AI bloons with reduced incomenote .
  • A crossover of BTD and Adventure Time called Bloons Adventure Time TD, which had soft launch access for selected continents on July 14, 2018, and was released worldwide on August 28 of the same year, with a PC release hitting Steam on January 16, 2019.
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All versions of the game could be played at NinjaKiwi's site until Flash reached end-of-life (though at the time of this writing they're working on a way around that), and the original BTD, BTD2, BTD3, BTD4, BTD5, BTD Battles, and Bloons Monkey City are available on the iPhone. A similar version of BTD3 is available on DSiWare. Bloons Tower Defense 5 is also available on Steam with extra content, and you can even buy it on the Switch. Bloons Tower Defense 6 was confirmed by Ninja Kiwi here and was released on June 15th, 2018 for Android and iOS, later getting a release on Steam and Amazon.

In the grand tradition of the Internet, the Bloons franchise has an exhaustively informative wiki right here.


The games provide examples of the following:

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    A-I 
  • Acid Attack:
    • The sixth game introduces the Alchemist tower, whose basic attack is throwing flasks of acid to deal Damage Over Time. Some upgrades allow his to throw stronger acid that deals damage faster, or create mini acid pools that damage bloons running over them.
    • The Glue Gunner starting from BTD 4 can make their glue corrosive with an upgrade. Other upgrades can make the corrosion stronger.
  • Allegedly Free Game:
    • Downplayed for at least the normal BTD games. While there is a good bit of premium content for BTD4 and BTD5, you can play the game very well without them. The Steam version costs $10 and has only skins as premium content. BTD6 averts this, costing money to buy on both mobile and desktop (while retaining in-app purchases).
    • Unlike the other games, Bloons Monkey City and Bloons Adventure Time Tower Defense are this trope. However, unlike most games, it very much is possible to play them without spending a single penny, but they will tell you about the premium items and currencies frequently.
  • All Your Powers Combined:
    • In BTD5, the Temple of the Monkey God will gain attacks and abilities related to all the towers sacrificed to it. For example, sacrificing a full power Ice Tower, Glue Gunner, Monkey Apprentice and Mortar will give the tower the ability to fire out exploding ice projectiles, corrosive glue blobs, giant tornadoes, and extra-powerful explosive missiles. All that along with the main Eye Beams.
    • In BTD6, not only does the TotMG return as the Sun Temple, but there's an even stronger variant of it known as the True Sun God, which can power up even more with further sacrifices. This makes it a recursive example of this trope.
    • Subverted by the Vengeful True Sun God. While it also sacrifices the two other tier 5 Super Monkeys, it doesn't gain either of their powers, instead only powering up its existing abilities.
  • And I Must Scream: Presumably the eventual fate of a bloon, if left unpopped:
    "If you were a bloon, wouldn't you rather get popped instead of slowly leaking and withering to an undignified husk? I guess we'll never know since they can't speak."
  • Animesque: The artwork of BTD5 has this look for some monkeys, especially the Ice Tower.
  • Anti Poop-Socking: One round tip in the fifth game is "Remember to occasionally take breaks and do non-BTD5 things." The sixth game has its own variation of this.
  • Appropriate Animal Attire: The Monkeys' choices of clothing cover the entire spectrum, from the completely naked basic Dart Monkeys, to the Fully Dressed Cartoon Animals like Quincy and Gwendolin. Usually, the higher the upgrade tier is, the more clothed the Monkey is. Notably, the series averts Pantsless Males, Fully-Dressed Females, like the explicitly female Adora wearing nothing but a cape.
  • Area of Effect: Ice Monkeys, Bomb Shooters, and Mortar Monkeys all create some sort of splash effect. Upgrades such as Ring of Fire, Fireball and Razor Rotors add splash damage to other towers.
  • Armor-Piercing Attack:
    • If one considers Lead Bloons to be armored, which are impervious to sharp-projectile towers, only certain types of attacks can actually break the Lead layer. Usually these are upgrades involving explosives, fire, corrosion, or simply upgrading the dart material to something of heavier construction.
    • Some upgrades do extra damage to Ceramic Bloons, such as Juggernaut for Dart Monkeys and Spiked Balls for Spike Factories.
    • The Alchemist's Perishing Potions and the Mortar Monkey's Shattering Shells remove the Fortified effect from Leads and Ceramics (and the latter can even remove it from low-tier blimps).
  • Arrange Mode:
    • From BTD4 Expansion on, there is the Deflation mode, which gives you 50,000 money at the beginning, but disables all forms of income, and starts you off at round 30 (21 in BTD4 Expansion).
    • BTD4 introduces the Harder Than Hard Apopalypse mode, which disables money income for progressing in between rounds, and removes breaks between rounds.
    • BTD6 includes a set of modifier modes for each difficulty setting on a map, with the difficulty and variety of modifiers increasing on higher difficulties. The Deflation and Apopalypse modes are included among these, as are ones that restrict your available towers, Reverse Mode (which had previously been added to BTD5), Half Cash, Double HP MOABs, Alternate Bloons Rounds (a much tougher sequence of rounds), Impoppable (formerly its own difficulty setting), and the hardest of them all, C.H.I.M.P.S. (no Continues, no Hearts lost, no Income, no Monkey Knowledge, no Powers and no Selling). Beating all of these variant modes is required for gold-bordering or black-bordering a map, and some have to be beaten before others can be unlocked.
    • BTD6 also introduces Races as a weekly event. Normally, a round only starts when the all the Bloons from the previous round are popped. In a race, however, the player can send the next round whenever they want. The goal of the race is to defeat all the rounds with as little time as possible.
  • Art Course: In 6, the map Cubism is based on the cubism art movement. The path forms zigzagging straight lines, separating the map into several areas, each with different colors.
  • Art Evolution: BTD2 and BTD3 used the same art style and assets as the first game, but the shift to BTD4 improved the graphics, and the art drastically changed for BTD5. BTD6 uses 3D models for the towers, some obstacles, and MOABs, and Bloons Adventure Time TD utilizes the same 3D model style.
  • Art Shift: The purchaseable profile icons in the Trophy Store are done in different art styles than the main game. For example, Brickell's is a black-and-white manga drawing, while the Transforming Tonic one goes into Deranged Animation.
  • Ascended Glitch: In BTD5, explosive towers that had their pierce buffed would increase the amount of time the exploding projectile could explode, rather than the amount of bloons the explosion could pop. While this bug was fixed on most towers, it persisted on the Hydra Rocket Pods of the Dartling Gunner. Come BTD6, and multi-explosion missiles are standard issue on the Rocket Pods.
  • Ascended Meme:
    • In March 2019, a Biker Bones skin was released for Striker Jones. Biker Bones was a recurring joke name for Striker Jones on the BTD6 subreddit.
    • In BTD6, the last Bloon to appear in round 5 of Alternate Bloons Round mode is a single Camo Regrow Red Bloon, in acknowledgement of the camgrow red memenote .
    • In Update 17, after months of making jokes about the Cave Monkey in the Frozen Over map and asking how to free him, the developers added a method to free him, and even made him his own tower unique to the map. And true to his alleged power, he can stun any bloon except for a BAD—yes, including a DDT or a ZOMG.
    • A common joke on the BTD6 subreddit is "Player 3" in co-op games being money-obsessed, wasting their money on Banana Farms and refusing to give money to other players. The Scream emote for co-op introduced in 21.0 mentions that it can be used to scream at Player 3 for not sharing their cash.
    • The "No Cash Drops" emote was spawned from complaints that players, most likely hackers, would repeatedly drop Cash Drops in co-op and end up making it way too easy.
    • "2TC" (beat a game of CHIMPS with only two towers) and "2MP" (beat a game of CHIMPS with one tower getting at least two million pops) challenges are popular among fans, and later recieved their acknowledgements in-game, being added as hidden achievements.
    • "Slons", a joke map submitted for a map contest, became a hit with fans. It got added as "Blons", with an identical layout, as a secret map in 24.0. This turned out to be an accidental content leak, as the way to access it was patched out so that Blons could be featured in an April Fools' Day daily challenge shortly after the update's release.
  • Asteroids Monster: Basically the whole premise of the game, and which sets it apart from most other tower defense games: every single bloon except for the lowest tier has one or more bloons contained within it. Short list from strong to weak in BTD6: A BAD gives 2 ZOMGs gives 4 BFBs which give 4 MOABs, which give 4 ceramics, which give 2 rainbows, which give 2 zebras, which give a black and a white, which each give 2 pinks, and from then on only one comes out each time, going pink, yellow, green, blue, red. The other thing the BAD gives is 3 DDTs, which give 4 Camo Regen Ceramics. Additionally, there's also lead bloons that give 2 black and purple bloons that give 2 pink. Also, if a bloon gets through your defenses, you lose lives equal to the total amount of bloons you let slip (ceramic and blimp layers also count as lives lost), meaning that if a blue one gets through, you lose two lives, but if a ceramic gets through, you lose 104 lives. BTD4 added the Red Bloon Equivalent (RBE) counter, which is Exactly What It Says on the Tin—showing how many Red Bloons you are actually popping in the current round.
  • Awesome, but Impractical:
    • The Temple of the Monkey God in the fifth game is a little half-and-half. It fires enormous beams capable of tearing anything less than a BFB to shreds, but it costs a whopping $125,000 (on Medium difficulty without discounts), since you have to buy other Super Money upgrades to even access it (and that's without the range upgrades—counting those, the price goes up to $127,500). It will also sacrifice any player-bought towers in its range and absorb their powers, to the point of becoming powerful enough to down ZOMGs as though they were red bloons, but that means you need to pay for the absorbed towers (and you'll need a ton of money to get it to maximum power). Of course, this is normally only used in freeplay because of its high costs; although it is perfect for the rounds where bloons gain extra movement speed and health, there isn't anything forcing you to use it.
    • Several of the tier 5 upgrades in BTD6.
      • In general, the final upgrades for money-earning towers such as the Banana Farm and Merchantman Buccaneer are so expensive that you won't be able to make a profit unless you're going for the super-late rounds.
      • Super strong, but very expensive tier 5 upgrades like Flying Fortress, Super Mines, and Ray of Doom. In a standard 100-round game, you can just sit back and wait for the victory screen after you purchase them. However, they're so expensive you'll never be able to get them without heavy farming. If you want to go into freeplay, you might as well get the Vengeful True Sun God, which is more expensive, but also way more powerful.
  • A Winner Is You: The messages you get when defeating the Bloons on a track and difficulty are this, with the most bland being whenever you win a map and difficulty that you've already completed in BTD6.
"VICTORY! You've stopped the nasty bloons[!]"
  • Bee Bee Gun: The Beekeeper, a Special Agent from the fifth game (and secret tower in the iOS version of the fourth), attacks by sending bees out of beehive to latch onto bloons for gradual damage.
  • Beam Spam:
    • Super Monkeys gradually get more beam-spammy as they upgrade, going from laser vision to plasma beams to the Sun God/Avatar (a Spread Shot of three sun beams) and culminating in the barrage of the Temple of the Monkey God. Then there's the Temple of the Vengeful Monkey unlockable ability, which lets the Temple shoot twice the amount of beams for a few seconds, and each beam is also more powerful.
    • The Robo Monkey shoots two laser projectiles per frame (one per arm) to the Sun God's 1.5, though without as much spread or precision. Its upgrade, the Technological Terror, fires the same amount of beams as the Robo Monkey, but its plasma is green and extremely deadly: a single stream of this green plasma is twice as deadly as a single stream of the regular purple plasma, but since it fires two streams of it...
    • The Dartling Gun's Laser Cannon upgrade makes it spam high-pierce laser beams. The following upgrades, Plasma Accelerator and Ray of Doom, turn it into a Wave-Motion Gun.
  • Bears Are Bad News: The Beekeeper is a bear and aggressively attacks bloons with his bees. Good to know that he's on your side.
  • Berserk Button: The Angry Squirrel, who goes berserk whenever a bloon leaks. His pro version gets a worse anger management problem, and it now gets pissed every 20 acorns it throws.
  • BFG:
    • Most military-based towers become one of these when fully upgraded, with appropriately powerful projectiles to fire from themselves.
  • Big, Bulky Bomb: The icon for the Monkey Ace's Ground Zero and Tsar Bomba abilities have this. Using the abilities causes the Ace to drop a massive bomb that damages the entire screen.
  • Blow You Away:
    • In BTD5, the Monkey Apprentice gets this quite literally with the Tempest Tornado upgrade, allowing him to blow Bloons back towards the start.
    • Downdraft on Heli Pilots blow bloons under the heli back to the enterance.
    • In BTD6 the Druid of the Storm inherits the tornados of the Apprentice. The final upgrade on the Druid's top path even lets it blow back MOAB-class Bloons.
  • Bonus Boss:
    • The BAD in modes outside of Impoppable and CHIMPS. It usually only appears in round 100, while most game modes only go up to round 80 at most. In Alternate Bloons Round mode (which only goes to round 80), you face a fortified BAD instead of a regular one.
    • If you make it all the way to round 200 in freeplay, which is only possible with heavy farming to buy very strong defenses such as a Vengeful True Sun God, you get to a special round made of 2 fortified BADs. Due to MOAB class health scaling with increasing rounds, those have no less than 1.3 million HP each, which is almost 50 times as much as the one on round 100. They're also considerably faster than normal due to speed scaling.
  • Boring, but Practical:
    • Banana Farms are expensive and don't attack Bloons, but they give you extra money, which you will need in later levels when the Bloons themselves earn you less money. The Monkey Bank upgrade is more so this, especially in BTD6 with its Banana Farm nerf. This exchanges generating bananas and spewing them out for generating and storing money inside its own bank, which also has an interest rate, meaning the more money is in there, the faster you gain money (until you reach its maximum limit). In the sixth game, if you have a 2-3-0 Banana Farm, you can reach its maximum limit of $7000 within 12 rounds, making it an easy way to get money.note 
    • Starting a map with three dart monkeys. They might not be able to lead to many exciting upgrades, but it's one of the most versatile starts in the game, able to beat the first few rounds even on multi-path maps while leading to upgrades that can hold you out until something more powerful.
    • The Glue Gunner. At first, it's a non-offensive tower which slows bloons, and isn't super-efficient at that, but it's so cheap that it can be placed early on to help other towers while conserving money. Putting enough into upgrading one allows it to either deal heavy damage-over-time to anything it coats with glue, spread glue across swarms of bloons and the entire screen, or stop MOAB-class bloons in their tracks.
    • The Spike Factory is simple and boring; no moving parts, just a constant stream of small piles of tacks. But it can be upgraded to pop lead bloons, there's a special option for ceramic bloons, and it can kill MOABs more quickly than a Super Monkey. The sixth game introduced the Perma-Spike, a fifth-tier Spike Factory that, even after some nerfs, still stands as one of the most useful fifth-tier towers despite doing nothing more than building a pile of high-damage spikes.
    • Quincy in BTD6. He lacks the ability to apply buffs on other towers, like Obyn and Brickell, and can't debuff bloons either, like Gwendolin, Ezili, and Benjamin. Even among the pure DPS towers, he hardly stands out, with Adora's sacrifices letting her reach her maximum potential early on, Etienne drone swarm allowing for attacking out of line of sight, and Churchill sporting more raw power. However, Quincy is one of the only heroes capable of starting a game, greatly aids during early rounds, and holds reasonable damage output even in late-game.
  • Boss Battle: Not formally called as such, but the rounds 40, 60, 80, and 100 invoke the feel of a boss battle, as each only consist of a single MOAB-class Bloon which is stronger than any Bloons you've faced in the previous rounds.
  • Boss-Only Level: A few rounds in the series have rounds in which only MOAB-class bloons (or other high ranked bloons) appear.
    • In BTD5, there is only one bloon in Levels 46, 60 and 85—the MOAB, BFB and ZOMG, respectively, which are introduced in said levels. Not the case for the latter in Impoppable difficulty, as you face five ZOMGs in Level 85.
    • The ending rounds of Easy, Medium, Hard, and Impoppable/C.H.I.M.P.S. difficulties in BTD6 are fights against a lone blimp. Easy has the MOAB on round 40, Medium has the BFB on round 60, Hard has the ZOMG on round 80 and Impoppable and C.H.I.M.P.S. have the BAD on Round 100.
      • In Alternate Bloons Rounds, round 100 is a single fortified BAD.
      • Round 200 in freeplay is a special non-random round made of 2 fortified BADs
  • Boss Rush:
    • Level 75 of BTD4, the final level of Hard mode on any course, is a long sequence of MOAB and BFB bloons and nothing else.
    • In BTD5, the final round on Impoppable difficulty has not one, but five ZOMGs.
    • Round 98 of BTD6 sends out 8 ZOMGs and 30 fortified BFBs.
    • Freeplay rounds from BTD4 onwards are essentially waves of nothing more than bigger, faster, and tougher waves of blimps. In BTD5, for example, later Freeplay rounds are immense waves of nothing but ZOMGs, while BTD6 gives a bit more variety thanks to the existence of the BAD, DDT, and the Fortified modifier.
  • Bowdlerise: The Cool Math Games version of the first game changes a pre-round message about the Super Monkey from "he really kicks ass!" to "he is really poptastic!".
  • Bread, Eggs, Breaded Eggs:
    • Black Bloons are immune to (most) explosives, White Bloons are immune to freezing, and Zebra Bloons are immune to both of these!
    • The pre-round comment for Round 59 in BTD6 has this with leads and camos.
      "Can you pop Lead? Can you pop Camo? How about... Camo Lead?"
    • An unofficial term for Bloons that have both the regrowth and camo properties combines the two into "camgrow".
  • Bribing Your Way to Victory:
    • In the fifth game, there are a lot of options for outright breaking the game for the payment of real money. They range from simple upgrades, such as dart monkeys getting an area of effect on the dart, which simply give towers more versatility or firepower, to buying ingame money (both Monkey Money and the cash required for upgrading towers) as well as lives.
    • The sixth game has the double cash mode from the fifth game, now costing 18 dollars instead of 10, and you can still buy Monkey Money, but you can also buy Insta-Monkey packs, which are pretty much this game’s version of loot boxes. Just like BTD5’s in-app purchases, however, they are entirely unrequired to enjoy the game. In fact, Insta-Monkeys are also given out rather generously through collection events, and double cash is the only thing you can't get through just playing the game.
    • BTD6 also brings the "Unlock All" ability, which instantly gives you all the upgrades for a selected tower. While they only cost USD $4.99, you can easily farm the XP needed for the upgrades. All real money purchases are rendered null by the CHIMPS difficulty modifier, which levels the playing field some.
  • Bullet Seed: The Watermelon Spitter Special Agent, a chipmunk that builds up watermelon seeds in its cheeks and spits them out as soon as bloons enter its range.
  • Call-Forward: The map Village Shore in BTD5 is a reference to the main menu of ''BTD6''. Note that this map was released exactly one month after the release of 6.
  • Cap: The fire rate of any tower cannot exceed once per frame. This makes Overclock and MIB Call To Arms useless on towers with certain upgrades (such as the Ray of Doom for the Dartling Gun, Technological Terror for the Super Monkey, etc.). Even worse (but possibly funny) is that towers that are (somehow) overclocked too much deal no damage to any kind of bloon!
  • Challenge Run: Many of the game modes involve special restrictions and rules:
    • Apopalypse (no breaks between rounds, no end-of-turn income)
    • Deflation (you start with a large amount of money, but can't earn any more)
    • C.H.I.M.P.S. (only one life, no powers, no Monkey Knowledge, Money Multiplier towers don't work, and you can't sell towers)
    • Single-class runs (Primary only, military only, magic only)
    • Double MOAB health
    • Half-cash
    • The daily challenges and advanced challenges offer a new set of rules each day, usually by limiting which towers you're allowed to use.
  • Changing Gameplay Priorities: In early rounds, you want to prepare against the various types of Bloons the game throws at you. As stronger Bloons can pop into multiple weaker Bloons, towers that can pop many Bloons at once are favored. In later rounds, however, piercing is no longer an issue and your main concern is having as much damage as possible against Ceramics and MOABs, because the game will start throwing a bunch of them. This gets exacerbated by the appearance of Super Ceramics, which are much tougher than regular Ceramics but only have one child.
  • Character Select Forcing:
    • It's impossible to win BTD2 without Cannons, because they're the only towers in the game capable of popping Lead Bloons.
    • Flooded Valley is a map largely covered in water, separated from the land by a large wall. If you're going to use a hero for this map, it's going to be either Admiral Brickell or Pat, as both can be placed on water, with Brickell also syngerizing well with water towers. While Adora's ability briefly gives her enough range to attack up the wall (and thus is the go-to for Primary Only on this map without using pontoon powers), it's rather inefficient, and Churchill is too expensive to be feasible despite his large range.
    • Spillway encourages CHIMPS players to start with a Ninja Monkey, since it's the only starting tower that is both small enough to fit in the middle barrel that allows it to attack bloons entering the track's middle circle, and can pack a decent amount of early popping power. The middle circle is surrounded by expensive-to-remove walls and a moat that hinder all other towers from reaching inside.
  • Checkpoint Starvation:
    • The Flash version of Bloons Tower Defense 5 did not allow you to save on Extreme-difficulty tracks. However, the mobile version permits saves there.
    • Usually, Bloons TD 6 autosaves after finishing any round except in Co-op, deleting the save upon death, a forced restart, or switching to a different mode on the same map. However, Hard Mode in the "Happy New Year's" Odyssey had merged sequences of up to eighty rounds into one round per island, meaning that if you exited an island for any reason, you had to restart the entire island from the beginning.
  • Chuck Cunningham Syndrome: Almost all the Special Agents in Bloons Tower Defense 5 do not return in 6, with only the two monkey-based Agents persisting over.
  • Color-Coded for Your Convenience: In BTD6, towers are divided into four categories, with each category having its own color, as well as another category for heroes. Primary is blue, Military is green, Magic is purple, Support is orange, and Heroes are yellow.
  • The Computer Is a Lying Bastard: The description for the Mortar Monkey's Artillery Battery says that its "Pop and Awe" ability doesn't affect MOAB-class bloons. Yet, it still stuns them against what the description says, though the stun is weak on anything stronger than a MOAB.
  • Computer Virus: At level 7, Benjamin, the Code Monkey hero in BTD6, writes Bloon trojan viruses, and when successfully sent to a Bloon, causes them to spawn no children (the Bloons in lower layers) when popped. The downside to this is that you don't get the money from them. This was eventually changed so that you receive the number of layers the bloon has in cash (so an infected rainbow bloon, having 8 layers, gives $8 upon being popped), so you get back something from popping it. You still lose out though.
  • Contractual Boss Immunity:
    • In the early games, MOABs and BFBs are immune to slowing down as well as the Super Monkey Storm (otherwise a One-Hit Kill). Later games would introduce more ways to slow and stun MOAB-class bloons, though these are typically reserved for high-tier towers.
    • In BTD5, there are a few special abilities which do nothing except for destroy a single MOAB-class bloon. However, the ZOMG, while not completely unaffected, will only take 1000 damage. When the sixth game introduced a tougher blimp, the ZOMG became So Last Season and some towers got upgrades that could instantly kill it.
    • The BAD from BTD6 is immune to all kinds of slowing or stun status. Other debuffs (such as debuffs that cause bloons to take extra damage from getting hit, such as Cripple MOAB, Super Brittle, and Glue Storm) can still affect it, though.
  • Cool Airship: Various blimps with acronym names appear as Bosses in Mook Clothing, with five different ones as of the sixth game.
  • Cool Boat: Two water-based towers exist in the games. The first introduced was the Monkey Buccaneer, a mid-price tower that can be upgraded into a fast-firing battleship that controls miniature fighter planes, an explosives-armed, grape-shooting pirate ship that can hook onto blimps to instantly kill them, and (starting in the sixth game) a merchant ship with massive income bonuses. The second is the Monkey Sub, which is cheap and initially weak, but can get an Advanced Intel upgrade to let it fire darts at bloons in the range of any towers. Its upgrades include a nuclear submarine that melts bloons in its radius (the sixth game lets it become an Energizer that reduces tower cooldowns and increases hero experience gain), a missile-bombarder with an ability that can One-Hit Kill a ZOMG (further upgradeable to let it fire strong missiles at any blimp entering the screen), and a Sub Commander that can boost the strength of an armada of subs.
  • Cosmetic Award:
    • There are hidden achievements in BTD6 that enable access to Big Bloons, Small Bloons, Big Tower, and Small Tower mode, where Bloons/Towers become bigger/smaller than usual. However, this is purely visual, as the Bloons/towers still retain their original hitbox.
    • The Trophy Store of BTD6, where you can exchange trophies obtained from Races and Odysseys for things such as player avatars, new music, new special effects, Bloon skins, etc. Items bought at the Trophy Store are entirely for cosmetic purposes and don't alter the gameplay.
  • Crossover: In Bloons Adventure Time TD, the Bloons invade the land of Ooo!
  • The Cracker: Benjamin, the sixth hero in BTD6, zigzags this. While he is a hacker who can create viruses, he's on your side and is happy to use his skills to get you more money and sabotage the Bloons.
  • Crutch Character:
    • Dart Monkeys in BTD5 upgraded to Triple Darts are very effective early on, but become far less powerful later in the game.
    • Monkey Engineers with the Sentry Gun upgrades are so cost-effective early game that one of the most common early-game builds in BTD5 is just to rely on that for the entire early game in order to farm money. Without Cleansing Foam, however, they can't do anything about Camo or Lead bloons. Engineers can remain useful throughout the game just for the sheer area they can cover, though they start to fall off in usefulness against MOAB-class bloons (unless you're positively covering the map with them).
    • Dartling Guns are one of the more useful towers as-is and can cheaply mow down all but the most thick clusters of bloons with some upgrades, especially with some good placement. However, once the first MOAB-class bloon shows up, they notoriously struggle to deal enough damage to the blimp layer fast enough to make a difference. This can be subverted with sheer numbers of Dartling Guns or several of the highest upgrades, though it would cost far more than just using towers better suited to MOAB-busting.
  • Damage-Increasing Debuff: Some debuffs allow towers to pop additional layers to affected Bloons, or just deal multiple damage to MOAB-class bloons. This type of damage is especially potent since it affects every hit of every projectile, and it's one of the few types of debuffs that can affect the BAD.
    • Embrittlement is a tier 4 upgrade for the Ice Monkey in BTD6. Bloons frozen by this monkey will pop an additional layer when attacked, but it can't freeze MOABs. The tier 5 upgrade Super Brittle allows the tower to target MOABs, as well as increasing the damage to four extra damage instead of one.
    • The BTD6 version of Sniper Monkey's Cripple MOAB upgrade allows it to not only stun blimps, but also increase the damage it takes by five. Against a BAD, the stun is ineffective but the damage increase still applies.
    • The 9.0 patch of BTD6 gave Glue Storm this ability. When the ability is activated, all glued bloons on the screen take an extra layer of damage.
  • Damn You, Muscle Memory!: An infrequent example of something not related to controls but rather gameplay; in BTD6, Hard mode actually starts you on round 3 instead of 1. Likewise, Impoppable starts you on round 6. This means that you have even less time to get extra cash!
  • Degraded Boss:
    • MOAB-class bloons are introduced in a boss-like fashion (facing one of them alone in the level they are introduced), but they quickly become regular bloons afterwards, up to the Freeplay levels, in which everything eventually spawns as the strongest MOAB-class bloon available.
    • Downplayed with the BAD in the sixth game. It first appears on round 100, but sparingly appears after that in Freeplay rounds as special encounters. You'll never be Zerg Rushed with BADs as opposed to, say, the huge stack of ZOMGs that appear two rounds before the BAD's first appearance (or the horde of 30 DDTs three rounds before that).
  • Depth Perplexion:
    • Presumably, the bloons are floating above the track, yet they are affected by spikes lying on the ground. And the Monkey Ace is flying even higher above them, yet its darts can pierce through bloons as if they were on the same level.
    • Taken a step further with the obstructions in BTD6. On some stages, towers will not be able to "see" past these obstructions if you place them in specific locations, meaning that they can't pop whatever's behind them, although some maps (such as Tree Stump) feature another level in which you don't have obstructions, which creates this as any projectiles should be higher or lower depending on where they're placed, yet still manage to pop the bloons.
    • The Heli Pilot's Razor Rotors upgrade uses the helicopter blades to shred Bloons, even though the helicopter is flying above the Bloons.
    • A mod that allows you to move the camera shows just how much more of this trope applies, most of which are hidden by the Fixed Camera angle. The projectiles' models don't even need to physically touch the Bloons' models to damage them.
  • Developers' Foresight: Churchill in BTD6 can utter "Protect that exit!" whenever the Bloons start to leak. In maps with multiple exits, this is changed to "Protect those exits!"
  • Difficult, but Awesome: Regrow farming, the specific strategy of exploiting the fact that you can make rounds last forever by pushing back regrow bloons, letting them regenerate, then pushing them back again, giving infinite time to activate cash producing abilities. However, this comes at the risk of the regrowing bloons multiplying to the point where your defenses are overwhelmed.
  • Difficulty by Acceleration: From Round 80 onwards, all bloons start moving faster (and tougher, in the case of MOAB-class bloons) with each passing round. They start moving even faster once you reach Round 110, where the round speed increase becomes higher.
  • Disc-One Nuke:
    • Monkey Subs have been considered a Disc-One Nuke ever since their introduction in the fifth generation of the franchise, due to their power for a player's buck. For instance, their Airburst Darts cost approximately $1000 but quadruples the projectiles fired at the bloons, and Twin Guns allows them to fire twice as fast for less than $500. (In comparison, comparable buffs for other towers cost thousands of dollars.) They also have an upgrade, Advanced Intel, that lets the subs use the targeting range of any other tower already placed on the map, and can also absorb the camo detection of other towers for merely $540. In Bloons TD 6 in particular, they can be buffed by alchemists to double their damage and add even more anti-blimp damage as well as lead popping capabilities, making submarines the go-to for Half Cash mode.
    • Berserker Brew and Stronger Stimulant, top path alchemist upgrades, essentially turn other towers into Disc One Nukes. These allow the alchemist to buff other towers' damage output significantly. These buffs include pierce, damage, range, and attack speed simultaneously and stacks with the Acidic Mixture Dip upgrade in the same path to provide extra lead, ceramic and blimp popping power. Stronger Stimulant in particular allows the alchemist to buff two other towers (or three with the Faster Throwing crosspath). Particular towers that these alchemists easily turn into Disc One Nukes include Bloonjitsu, bottom path Tack Shooters, Spiked Balls, and Monkey Subs.
  • Do Not Touch the Funnel Cloud:
    • The Monkey Apprentice's tornado magic can blow quite a few bloons back, but it only affects the ones it touches directly. The winds are, however, strong enough to remove ice and glue from blown bloons. Be careful when using wizards with the tornado upgrades in levels with regrowth bloons; if these bloons are not popped quickly upon being blown back, the will regrow into massive armies that rush past your defense.
    • In BTD6 the Druid gains this ability instead, and its final upgrade, Superstorm, can even blow back MOAB-class Bloons!
  • Doomy Dooms of Doom:
    • One of the Daily Challenges for BTD5 was called Rainbow Rush of Doom.
    • The Ray of Doom, a fourth/fifth-tier upgradenote  for the Dartling Gun, which can destroy any and all non-ZOMG bloons in seconds.
    • Bloons TD 6 introduces the Big Airship of Doom. It has the second-highest HP count of any bloon introduced in the main series (the absolute highest goes to the "Test Bloon" you can only find in Sandbox), and is immune to any slowdown or knockback effects that affect other MOAB-class bloons.
  • Double Unlock: In BTD5, you unlock a weapon's upgrade path via having a high enough rank, and the tower class needs to be at a high enough level.
  • Dummied Out: In BTD6, all the bloons have fortified sprites, despite the fact that only Leads, Ceramics and MOAB-class bloons can have them in-game.
  • Dread Zeppelin: The most powerful bloons are the MOAB-class bloons, huge and often slow blimps that take a lot of damage just to pop their first layer.
  • Dwindling Party: In Odyssey Mode, you can only take certain number of towers with you to complete a series of maps. In Extreme Odyssey Mode, the towers you use in one map will be unusable in the next.
  • Early Game Hell:
    • TD 6's Alternate Bloons Rounds mutator for Hard Mode has this in spades. The premise of the mode is that more powerful than usual Bloons will spawn in each round. This means that the early game will be frought with lead and camo Bloons that you'll be hard pressed to have towers even capable of popping without resorting to powers or instamonkeys. Once you reach wave 20 or so, it's not much more difficult than regular Hard Mode.
    • The Apopalypse game mode also has a case of this, because you don't get any end-of-round cash bonus, which usually is a large portion of your income early on. However, once you've reached midgame, you get enough cash from popping Bloons and/or farming such that the lack of the bonus becomes insignificant.
    • In general, the way harder maps are designed tends to more heavily up the challenge of the early game than the late game. Harder maps prefer to use multiple pathways and undeployable terrain to spread the player's towers thin over a large play area. Late game, the player has enough money and towers to meet the needs of several pathways at once, but the early rounds require fending off several waves of bloons with only a few dart monkeys or tack shooters, and it will be a while before mapwide covering towers like Mortars or Helicopters become reasonable to buy.
  • Early Installment Weirdness: Bloons Tower Defense 4 introduces camo bloons. However, in this game, the camo bloon is a specific type of bloon, rather than a property that any bloon can have. Additionally, camo bloons can be affected by collateral or splash damage from any tower, while in other games, they completely ignore attacks from towers that don't have camo detection.
  • Easter Egg:
    • You may not want to tap BTD6's heroes too much in a short period of time... Gwendolin sums it up as well.
      "I wouldn't do that if I were you."
    • However, you may want to try tapping the buildings on the menu screen; you may see a few monkeys pop up!
    • Another nice attention to detail is that the village clock on both the menu and in gameplay match your system clock.
    • On the map Candy Falls in BTD6, there are clickable spots that cause an Oompa Loompa monkey to run around. Clicking them in the right order makes the Oompa Loompa song, and also unlocks Small Towers.
    • If you summon the True Sun God while Adora is at max level, she will get a buff that makes her attacks three times stronger. Her visuals also change. She has a different pose, her eyes glow, and she gets an elaborate headdress in the shape of the sun.
      If you summon the Vengeful True Sun God, on the other hand, Adora will transform into a red and black version of herself. If you do this while in Adora's Temple, the entire map will grow darker and the temple itself will also change into red and black.
    • In the map Frozen Over in BTD6, there's a caveman monkey frozen inside the ice. Previously it was just a decoration, but in later updates, you can free it as a secret tower, referencing memes about freeing the monkey. You need to target the block he's frozen in with Mortars. Once freed, the Cave Monkey will be placed randomly on the map. His damage is weak, but he can stun anything except a BAD.
  • Easy-Mode Mockery:
    • The picture for easy mode in BTD4 onwards is a baby monkey.
    • Subverted on Extreme difficulty tracks on BTD5. The Easy mode is merely a Point Five Oh Sniper Monkey, the Medium being a Ray of Doom Monkey, and the Hard mode is a Sun God Monkey. You know it's Extreme when the easy mode pic is a badass (although not as badass as the other two).
  • Elite Mooks: Ceramic Bloons, the strongest of the regular Bloons. Unlike weaker Bloons which can only take one hit before popping, a Ceramic Bloon can take 10 hits before popping into Rainbows. In addition to having multiple hit points, Ceramics are also fast, being the fourth fastest regular Bloon, just below Pinks, Yellows, and Purples. Past round 80, Ceramics also turn into Super Ceramics, which have a whopping 60 HP in exchange for only leaving a single descendant when popped.
  • Excuse Plot:
  • Everything's Better with Monkeys: The protagonists of the game are monkeys, originating from the lone dart-throwing monkey in the original Bloons game. By the sixth Tower Defense title, monkeys of all shapes, sizes, and abilities make up most of the player's defenses, with everything else either being machines, buildings, or the animal Special Agents.
  • Everything's Better with Plushies: One of the monkeys, the Super Monkey, has a currently discontinued plushie version.
  • Exactly What It Says on the Tin:
    • The Beginner-level map "Three Times (3x) Around" in BTD5, in which bloons circle the central loop, well, three times. This gives your towers two additional chances to catch bloons, but heavier bloon overlap makes it more difficult to know if bloons are about to escape.
    • In BTD6 we get Four Circles, which is a track comprised of four circles that the Bloons go around before exiting. To give it a bit more flavor, it's styled after a track-and-field course.
  • Eye Beams: The Super Monkey uses these as upgrades. First it uses lasers, then plasma, and then sun rays.
  • Fanboy: One of the final upgrades for the Dart Monkey turns it into a Super Monkey Fan Club. It gives it the ability to turn itself and nearby Dart Monkeys into actual Super Monkeys for a few seconds. BTD6 has the Plasma Monkey Fan Club, which turns nearby Dart Monkeys into 2/0/0 Super Monkeys with increased pierce, attack speed, and damage instead of mere 0/0/0 Supers, and can also affect 20 Dart Monkeys instead of just 10.
  • Floating Continent: The Floating Islands and Ascension tracks in BTD5 Deluxe feature these, but the islands in Ascension are clouds.
  • Fun with Acronyms:
    • The games have a lot of them, notable examples being the names of the MOAB-class bloons.
      • The MOAB, also known as Massive Ornary Air Blimp. As for BFB, it's Brutal Floating Behemoth.
      • The ZOMG is the Zeppelin Of Mighty Gargantuanness.
      • The DDT stands for Dark Dirigible Titan.
      • The BAD from Bloons Tower Defence is the Big Airship of Doom.
    • One stage in BTD3 has the hint "MOAB stands for Massive Ornary Air Blimp, not Mother Of All Bloons. Either way, it brings pain."
    • From the fifth game's fandom comes NAPSFRILLS, which means No Agents, Premiums, Specialties, Farming, Road Items, Lives Lost or Selling.
      • The first three refer to the out-of-gameplay boosters like special agents, premium upgrades, and specialty buildings.
      • "No Farming" means no method of cash gain other than bloon pops. YMMV, but the 3|x village (Monkey Town) is debatable in this respect.
      • No Lives Lost can be a challenge on its own, but prohibiting spikes and pineapples ups the ante. Not selling towers goes further still by denies money and space refunds, meaning that careful placement and upgrading is required.
    • Any variant of NAPSFRILLS, including NAPS, NLL, and NAPS NLL, can be used not only for normal maps, but special missions, daily challenges, and random missions as well.
    • CHIMPS in BTD6 is short for No Continues, no Hearts Lost, no Income, no Monkey Knowledge, no Powers, and no Selling".
  • Fuuma Shuriken: Boomerang Throwers can be upgraded to use these in BTD3 onwards, though the game refers to as glaives. In BTD5 and onwards, they can also upgrade to homing fuuma shuriken, and then get two of them that permanently rotate around them, shredding anything that gets close.
  • Fragile Speedster:
    • Pink and Yellow bloons. They are the only bloons in the entire series that are faster then the Ceramic Bloon, but they only have 5 and 4 layers respectively.
    • The DDT is definitely one of these with its rapid speed that's comparable to the pink Bloon (not to mention its lead and camo properties) but it's by far the second weakest MOAB-class bloon in terms of health, being taken down with only 924 hits. Of course, it is far more difficult to damage a DDT in the first place thanks to its wide range of immunitiesnote  than to take it down once you can damage it.
  • Game-Breaking Bug:
    • Attempting to move Pat Fusty via the Chinook ability while any submarines are underwater will outright crash Bloons TD 6.
  • Game Mod: Several YouTubers have created and even distributed (now discontinued) mods for the Steam ports of BTD5. Here are some examples:
    • For BTD5 Steam, there's Revenge of the Bloons, which has changes such as faster juggernauts and glue being able to hit MOABs, However, the most notable change is that there are fewer rounds to complete on all difficulties, but the game is a LOT harder. In fact, it makes Impoppable Mastery nigh-, if not outright, impossible to complete NAPS, and still quite brutal with anything short of Double Cash!
    • Junior Monkey modded an SWF of BTD5 Flash to add Mastery Mode from the mobile and Steam releases, camo-removing Viral Frost, glue that affects MOABs, and ice wizards. The latter freezes normal bloons while popping them (like directional Snap Freeze) and can conjure Absolute Zero, only it can stall MOAB-class bloons as well!
    • He has since created a No Escape (Flash) mod, which makes the game like BTD5 Mobile/Steam's No Escape mission, in which the map has no exit, instead looping infinitely around itself. The upshot is that you lose 1 life per second if the bloons remain onscreen for too long. Specifically, this mod only contains tracks with loops in them (such as 3x Around and Countryside), and the game starts subtracting lives five seconds after the last bloon spawns, rather than 30 seconds into the round.
    • The Apopalypse Expansion mod, which gives Apopalypse rules (non-stop, no between-round cash) and pseudorandom bloon progression to the standard difficulty modes, with differing bloon progressions based on difficulty. The original Apopalypse mode is turned into the Harder Than Hard Impoppable difficulty like from BTD5 mobile/Steam, but even harder due to MOAB-class bloons having both double health and double speed! This will be really easy...
  • Gameplay Automation: Later games have an option in the pause menu to let the rounds to advance automatically without having to confirm them each time.
  • Game Plays Itself: In Apopalypse mode, the rounds advance automatically with no option to stop this in-game, even if there are bloons from the previous wave still on the map. Some versions allow you to save your game and come back between rounds, somewhat defeating a major part of Apopalypse.
  • Golden Super Mode: The "Sun" path of the Super Monkey. Harnessing The Power of the Sun, it shoots golden eye beams and towers from this path are golden in color.
  • The Goomba: Red Bloons. Slow and only takes 1 shot from anything to pop. It's the first type of Bloons you encounter in any game.
  • Guide Dang It!: Has its own page.
  • Guilt-Based Gaming:
    • In the Flash version of BTD5, the game displays this message when you try to quit a level: "If you quit, the bloons win!"
    • One of the messages shown between rounds in the second game tells the player they may not need to use every single type of tower to complete the game, but to think of all the programming and artwork that would be wasted if they didn't.
  • Harder Than Hard:
    • Extreme Mode in BTD5 is a map difficulty reserved for what are usually considered the three hardest maps in the game: Main Street, Bloontonium Lab, and Tar Pits (unlocked at Rank 50, Rank 55, and Rank 60 respectively). The maps cost a fee of either 25 or 50 Monkey Money per play depending on the map you choose, and will reward you with insanely large amounts of XP and an achievement worth many Awesome Points. Playing these maps can be a big risk if you plan on investing lots of Monkey Money into upgrades, Specialty Buildings, and Special Agents.
    • Impoppable mode. Towers and their upgrades are very expensive (including their sell price being reduced), the bloons move even faster, MOAB-Class Bloons are absurdly strong, and you only get one life. Speaking of the latter, it's impossible to have more than one life. Also, there are 5 ZOMGs on Round 85 just to screw you over.
    • Mastery Mode, currently only in the fifth game. All bloons are one rank higher, but you don't get extra cash! Overlapping with Nintendo Hard, this is a mode of play rather than a standard difficulty. Translation: it can be played alongside Impoppable difficulty! Hope you're good at the game if you dare take it on, especially on the harder difficulties.
    • Bloons TD 6 has six Harder Than Hard modes, enough to form an actual Tech Tree with its Standard Hard mode.
      • Alternate Bloon Rounds, the first of the bottom branch of the tree. The game says it itself in one of the tooltips: "You know 'alternate' just means harder, right?" It spawns tougher types of bloons at earlier rounds than usual; for instance, vastly more camos appear early on, and Round 40 contains a fortified MOAB (which normally doesn't appear until 22 rounds later in Standard) which has doubled health and drops double-health ceramics upon death. Also, if you attempt to Freeplay, you will be slapped with a fortified BAD on Round 100 (which normally doesn't appear until one hundred rounds later in Standard).
      • Impoppable mode makes a return in Bloons TD 6 as the second mode on the bottom path. Not only are towers and upgrades even more expensive than on Standard Hard, you have only one life (the Mana Shield Monkey Knowledge formerly also gave 25 regenerating extra lives in Impoppable until it was nerfed to be disabled here). You also have to beat rounds 81-100 on top of rounds 6-80, with those last 20 rounds being blimp-infested rounds that introduce the DDT and the BAD.
      • The final mode on the bottom path is C.H.I.M.P.S. You can only play it in a track after you defeat Impoppable mode (which in turn requires you to clear Alternate Bloon Rounds and the standard hard mode), which alone should say its difficulty. Not only are you unable to use any continues, you can't lose any hearts, you can't earn extra income (so much for Banana farms), you can't use powers, your Monkey Knowledge is disabled, and you can't sell your towers. You also have to beat rounds 6-100, like in Impoppable mode, with these restrictions (but thankfully the upgrade prices are the same as Standard, not Impoppable). The game even labels this as "the true test of a BTD master". Good luck.
      • Magic Monkeys Only, the first mode on the top path, only allows you to use Druids, Ninjas, Wizards, Super Monkeys, Alchemists, and a Hero Unit to beat what would otherwise be Standard Hard Mode.
      • Double HP MOABs is the second mode on the top path, where all blimps have doubled health, and this stacks with the Fortified modifier that already gives double health in the first place.
      • Half Cash mode is the last mode on the top path, and it deserves its spot. All gaining of money, from Bloon popping to Banana Farms is halved. This includes cash gained from the Cash Drop power. This mode is far more difficult than someone who doesn't play tower defense games might think—it’s been jokingly called "Insta-Monkey" mode, as the mode is made a lot easier by using Insta-Monkeys. It used to be Half Starting Cash, and came between Magic Monkeys Only and Double HP MOABs; this upgraded version of the mode became so difficult that switched places with Double HP MOABs!
  • Hazmat Suit:
    • The Glue Gunner starts wearing one once his glue starts splashing or gets corrosive.
    • Mortar Monkeys will get one when upgraded to Bloon Buster.
    • Dartling Gunners will also start wearing one once they get upgraded to lasers.
  • Heavily Armored Mook: Fortified Bloons. This trait gives Ceramics and MOAB-class Bloons twice the health, and makes Lead bloons take four times as many hits to pop. Their appearance even changes to look as if they're wearing banded armor.
  • Helicopter Blender: The Heli Pilot's Razor Rotors upgrade functions as this, chopping up layers of any bloon within the Heli's hitbox. This conflicts somewhat oddly with Pursuit targeting (the preceding upgrade), since most bloons won't get hit by the blades if the Heli is staying in front of them like how Pursuit targeting enforces.
  • HP to 1: A variation in BTD6. The Bloon Master Alchemist can throw potions that turn any bloon into a Red Bloon, including the ZOMG. It comes at the cost of not getting the cash from popping the bloons normally, though.
  • Humongous Mecha:
    • The Technological Terror is pretty big compared to most other towers, and it's a robot. It also has green plasma that's stronger than the usual purple plasma. Its final upgrade in the sixth game is even stronger, able to destroy ZOMGs like they were nothing.
    • The final upgrade of the middle path of the Dartling Gunner eschews its Macross Missle Massacre for a mech suit with two BFG missile launchers.
  • Hydra Problem: If a Regrowth Pink or stronger is not the original color, and if it regenerates, the new color will still contain as much bloons as it did before. This means that regrowth bloons must be damaged quickly, or they will swarm your defense and easily make you lose. The Monkey Apprentice is notorious for causing this with its lightning upgrade and both tornado upgrades. This feature can be Exploited to make round time indefinite for Supply Drop Sniper farming, or to grind money and Experience Points.
  • I Am X, Son of Y: Quincy, the first hero from BTD6, periodically says that he's "Quincy, son of Quincy" if you tap on him.
  • Infinity +1 Element: In BTD6, some upgrades change the tower's damage type into the "normal" damage type, which can pop all Bloon types. In some cases, this is granted implicitly without telling the players, like The Tack Zone, which can pop Lead despite its projectiles not looking any different from its previous upgrades (which are "sharp" types that can't pop Leads).
  • In-Game Banking Services: The 2nd path upgrade for the Banana Farm is called the Monkey Bank. It gains in-game money over time and this money can be withdrawn at any point. If you build multiple Monkey Banks, you can withdraw all their money at once. They can be further upgraded into the IMF Loan and Monkeynomics, which have higher carrying capacity and allow you to loan out some money, although you have to pay it back. There's also a Monkey Knowledge upgrade that lets you deposit money into Monkey Banks and their upgrades, to get even more later.
  • Instant Bandages: In BTD5, the ZOMG has a bandage appear over its skull design in its last stage of health.
  • Invisible Monsters: Camo Bloons aren't really invisible, but most towers will not be able to detect them unless there is a specialized tower nearby. However, several towers can be upgraded to have camo detection, while the Ninja Monkey, Spike Factory, and Dartling Gun (in BTD5) innately have this. In the fourth game where they were introduced, camos only existed as a single layer, and they could be hit by any tower, just not targeted by most; stray projectiles could still break camo layers, making them a lot less threatening so long as one can be hit to start a chain reaction.
  • Irony: Lead Bloons can only be popped with explosions (not counting upgrades such as the Monkey Apprentice's Lightning Bolt or the Super Monkey's Plasma Vision). Lead Bloons contain Black Bloons, which are immune to explosions, nullifying the towers unless they are near a support tower that enables nearby towers in its radius to pop all bloons, such as the Monkey Intelligence Bureau.

    J-R 
  • The Juggernaut:
    • The final upgrade for the Dart Monkey's tier 1 upgrades in BTD5 as well as the 4th upgrade of the first path in BTD6 is called Juggernaut. As the name implies, it's an unstoppable large spike ball that hits through all Bloons in its path before despawning (up to 104 bloons), including Leads and Ceramics. In the sixth game, it can be upgraded to the Ultra-Juggernaut, which shoots even larger spike balls that can split into multiple Juggernaut balls.
    • The ZOMG. You can't nuke it without a First Strike Capability, but must kill it with 4000 cuts.
    • Lead Bloons if you don't have appropriate defenses—not even a whole map of Aircraft Carriers can scratch it. However, just one explosive will do the trick.
    • The BAD. It has seven times the health of a ZOMG by the time you encounter it, moves at the same speed as one, and can't be slowed or stopped.
  • #HashtagForLaughs: The expert map #OUCH in BTD6 is actualy shaped like a # sign. Each line is a path for Bloons, making four relatively short paths. Let's say the name and difficulty are appropriate.
  • Hoist by His Own Petard: Zebra and stronger regrow bloons (up to ceramic) pop into two bloons that will each regrow into two of the original bloon, which can then each be popped and allowed to regrow into four of the original, and so on. A monkey with an ability that sends bloons back can allow them to multiply indefinitely, until the point where the bloons become dense enough that the ability can't affect them all, releasing a rush of high-level bloons past your defenses.
  • Kill Sat: The Bloonsday Device, one of the Special Agents in the fifth game. When placed on a map, it can perform an activated ability that summons a laser beam strike that can be guided with the mouse to fry any bloons it touches.
  • Kung Fu-Proof Mook:
    • Lead Bloons are immune to sharp objects but are vulnerable to explosions and energy-based attacks like lasers, plasma, fire, and magic.
    • Purple Bloons are the reverse—they're immune to energy-based attacks, but are vulnerable to sharp objects and explosions.
    • Black bloons take no damage from explosions, white bloons can't be frozen, and zebra bloons aren't affected by either. The ice immunity is a bit of The Artifact since these bloons were introduced when Bomb Shooters and Ice Towers were the only explosion/freezing sources in the game; by the fifth game, many towers can produce explosives but freezing is still exclusive to the Ice Monkeys, meaning that black bloons are much more intimidating than white ones.
    • DDTs combine the traits of Lead, Black and Camo bloons. They can only be damaged by glue, ice or magic attacks—and none of the towers with that kind of attack can detect Camo bloons without upgrades. That makes DDTs immune to every unupgraded tower that is not supported by a nearby Monkey Intelligence Bureau.
  • Level in Reverse: BTD5 and BTD6 feature a Reverse Mode modifier to make bloons go from the exit(s) to the entrance(s). In BTD6, the bloon send order is also reversed.
  • Lightning Bruiser:
    • Ceramic Bloons can take a lot of damage to pop, but unlike the understandably slow MOABs, BFBs, and ZOMGs, they are fast. They take 104 lives when they leak, which is a One-Hit Kill on Hard and a two hit kill otherwise. Super Ceramic Bloons in BTD6 only leave one child bloon, but they have six times the health of a standard Ceramic. And they can be Fortified for double health as well.
    • The Lightning Bruiser equivalent of the MOAB-class bloons is the DDT that debuted in Bloons Monkey City, which is slightly tougher than the basic MOAB, while being drastically faster and having an immunity to sharp objects and explosions. It is zig-zagged in that by the rounds they start appearing, everything below a ZOMG or a Fortified BFB is very easy to pop, but DDTs are very difficult to hit in the first place as inadequate Camo countermeasures can make them leak before the player can react.
    • All MOAB-class bloons become Lightning Bruisers later on, because the bloons eventually start to speed up, so you might encounter ZOMGs that are as fast as pink bloons!
    • BTD6 introduces the Fortified trait that puts Ceramic and stronger bloons into this territory, as their health is doubled, making them exceptionally tough, while moving as quickly as their regular versions.
    • For the monkeys, we've got the Super Monkey: it fires quickly, has good range and kicks a whole lot of ass. It becomes that much more powerful and awesome when upgraded.
    • There's also the Spectre, which fires darts and bombs at an alarming rate.
  • Limit Break:
    • Super Monkey Storm for the Monkey Beacon in BTD3 and 4 wipes out all non-MOAB bloons in one fell swoop, but costs $1,000 per use on Medium; not to mention it has a rather lengthy cooldown in 4. Interestingly, this becomes a special agent that in 5 that costs monkey money to use once but can damage MOAB-class bloons. It used to be able to One-Hit KO ZOMGs before a nerf that merely made it damage them. As an agent, it also has no placement cooldown, meaning you can spam as many as you can afford if you wish.
    • Every tower in BTD5, bar the Banana Farm, has an activated ability that is unlocked with the 4th tier upgrade on the right path. Most abilities can be used right away and all are free to use once unlocked. Like BTD4's Super Monkey Storm, you still have to watch for the cooldowns; rapidly buying and selling towers for their abilities here can circumvent the cooldowns, but also drain your cash rather quickly.
    • BTD6 puts activated abilities on the fourth tier of the middle path for most towers exceptions , with the fifth-tier middle upgrade either upgrading the ability, adding a new one, or providing a related buff. It gives even Banana Farms an activated ability, which grants you a loan which you have to pay back.
    • Also in BTD6, Hero Units also have two to three abilities, one unlocked at level 3 and the other at level 10. A few heroes have three abilities, one of which is unlocked at level 7.
  • Loads and Loads of Loading: Early versions of BTD6 would have a loading screen longer than a minute before the game starts.
  • Macross Missile Massacre:
    • In BTD5, the Bloon Area Denial System upgrade of the Dartling Gun fires a spread of three missiles with the rate of fire of a Gatling gun. Alongside this, the tower has an activated ability that shoots out two waves of 50 missiles.
    • Replacing the3 Bloon Area Denial System in BTD6 is Rocket Storm, which only has a single stream of missiles, but makes up with a longer lasting and more powerful swarm of missiles when the ability is used. These missiles are upgraded into mini-nukes if the Dartling Gun is upgraded to M.A.D.
  • Magikarp Power: As a rule of thumb, towers which are unreliable when unupgraded end up having the best upgrades:
    • The Tack Shooter. In the beginning, they really Can't Catch Up, since they shoot in an AoE spread instead of targeting. Once you unlock Ring of Fire or Blade Maelstrom, however, they're very unlikely to miss most things and have heavy strength, and the sixth game lets it become The Tack Zone, one of the most reliable fifth-tier towers available.
    • The Monkey Apprentice starts out with the same power as a Dart Monkey and more than twice as expensive, but once it gets the Lightning Bolt spell it can demolish clusters of bloons, Camo or not, and once fully upgraded it casts enough types of spells to do the work of four towers at once. BTD6 lessens its ability to spam spells but buffs each path with useful abilities like rapid-damaging walls of fire, a camo-decloaking energy wave, or just buffing the standard magic blasts to being MOAB shredders.
    • The Monkey Ace and Boomerang Throwers are sort of random and will rarely hit more than a couple bloons unless they're lined up right... until they're upgraded with either homing shots or enough dakka that nothing can get past them.
    • Dart Monkeys in BTD5 are just starting towers like in previous games, but their Super Monkey Fan Club ability can turn a cluster of them into a powerful force. BTD6 gives individual Dart Monkeys more potential to stand out, with their inexpensive fifth-tier upgrades like Ultra-Juggernaut and Crossbow Master being pretty useful for at least the main 80 rounds.
    • Glue Gunners. They start out doing nothing more than slowing single bloons down for a brief period of time, but the tier 5 top path shreds the notorious super-ceramics, the tier 5 middle path mass debuffs bloons to make them take more damage, and bottom path tier 3 cheaply slows MOAB class bloons down noticably.
    • Even Monkey Village joins in the fun for its left upgrade path, which gives its radar a deadly lightning attack that does a lot of damage. This was changed into Primary Expertise in BTD6, but it's no less deadly, with its Mega Ballista being one of the strongest single projectiles in the game.
  • Meaningful Name:
    • Churchill, the tank-driving hero in BTD6, is named after the Churchill tank.
    • Benjamin's focus is on getting you more money. "Benjamins" is a slang term for US $100 bills, which feature Benjamin Franklin's portrait.
    • The word "Sauda" means "fight" in Korean, and the hero Sauda is a swordfighter with a Korean-inspired design.
  • Marked Bullet: The Spectre's artwork in BTD5 features two mortars marked with "TO: BLOONS; FROM: ACE".
  • Meta Power-Up:
    • From BTD4 onwards, the Banana Farm and its upgrades allow you to obtain more money by various ways. It doesn't contribute directly to bloon-popping, but the extra money it generates can be used to buy more towers and upgrades.
    • In BTD6, the "Mo' Monkey Money" knowledge lets you get more Monkey Money for clearing a map, thus letting you unlock heroes or other Monkey Knowledges faster.
  • Metal Slime: The Golden Bloon in BTD5 and BTD6 only appears on a few maps every day, moves incredibly fast, and is hard to pop. Destroying it will reward you with some free Monkey Money.
  • Metropolis Level: In Bloons Tower Defense 6, one Advanced map is called High Finance. It's set in a city with a lot of under-construction buildings. If you pay some in-game money, you can finish them and place towers on them. The Bloons follow a road path in the shape of a dollar sign.
  • Mighty Glacier: With the exception of the DDT, all MOAB-class bloons are extremely slow at first (Red bloons are the same speed as a MOAB; the rest are even slower), yet much tougher than Ceramic bloons—they get even tougher (and faster) the further you go on Freeplay mode.
  • Missing Secret: The "Encrypted" map in BTD6 was promoted as having a big secret behind it. Between the intriguing ancient-style design and the title, fans were quick to experiment and try to figure out what the secret was. However, nothing ever came out of this. The map's only gimmick seems to be the panels that only a certain tower type can be placed on, but that's rather obvious. Exactly what the secret is on Encrypted, if it isn't the panels, remains unknown.
  • Money for Nothing: Averted with the in-game cash, which is reset for each game and is needed to place towers, but played straight with Monkey Money, the permanent currency. In BTD6, after you've bought all heroes and skins (which are permanent purchases), there's nothing to spend Monkey Money on except buying Powers and Continuing games. Even then, Powers are dirt cheap and not used that much, while the game isn't hard enough to require many Continues. Just to seal it in, many custom challenges as well as CHIMPS mode disables both Powers and Continues. Race retries and later higher-tier monkey knowledge were then made to cost Monkey Money as another attempt to further deflate the Monkey Money supply.
  • Money Multiplier: Many have been gradually introduced throughout the series.
    • Bloons Tower Defense 4 introduced the Banana Farm, which gave you extra money after a round finishes. It was majorly reworked in the fifth generation onwards to now give the player bananas worth small amounts of money that are thrown over the duration of a round instead. The player must manually pick up the bananas from the ground, and the bananas disappear if you do not do so.
    • Bloons Tower Defense 5 introduced:
      • Supply Drop, an activated ability for the Sniper Monkey that allows them call in airplanes that drop between $500-1000 per call. In the fifth generation, this ability could be used any amount of times as long as it's recharged, allowing it to generate infinite money via regrow farms.
      • Monkey Town, which multiplies the cash you get by popping bloons with the towers under its radius by 1.5.
      • Monkey Banks and Banana Investment Advisories, right-path upgrades for the Banana Farm which generate small amounts of money each round and then applies compound interest to the money currently in the bank when the round finishes. The money can be withdrawn at any time.
      • Support Chinook, the tier 4 Heli Pilot upgrade, gives you an ability that alternates between dropping extra lives and cash-giving crates when activated.
    • Bloons TD 6 added even more income generation sources on top of upgrading the existing sources.
      • Alchemists' bottom path contains two upgrades that fall under this trope. The tier 3 upgrade Lead to Gold gives you an extra $50 per lead bloon hit by the alchemist. The tier 4 upgrade, Rubber to Gold additionally throws a gold-making potion that triples the cash you receive from popping the non MOAB-class bloons hit by it. The cash received by Monkey Pirates and the Pirate Lord upon instantly killing blimps hit by the gold potion is also tripled.
      • Druids have the tier 4 Jungle's Bounty ability, that gives you an amount of cash that scales with the amount of farms near the Druid. They also possess the tier 5 Spirit of the Forest upgrade, that additionally gives $1000 when a round finishes.
      • Buccaneers gain a bottom path that starting with the tier 3 Merchantmen, give cash when the round is finished. This amount increases when it is upgraded to the tier 4 Favoured Trades, and is increased even further with the Trade Empire tier 5 upgrade, which increases the amount that Merchantmen generate by the amount of Merchantmen on the screen. The Merchantmen's money generation can also be boosted by 10% with the Central Market upgrade for the Banana Farm.
      • Supply Drop and Support Chinook gain their corresponding Tier 5 upgrades, Elite Sniper and Special Poperations, that not only increases the money their cash drops give, but augments their attacks as well (Elite Sniper with an attack speed boost, Special Poperations with a new offensive ability).
      • The Banana Research Facility can now have their crate values be increased by 25% via the succeeding Tier 5 upgrade, the Banana Central.
      • Benjamin is a hero dedicated to being a Money Multiplier - his very first skill giving you at least $150 after a round finishes, which can be increased by upgrading Benjamin. He also has a skill that allows Monkey Banks to fill faster.
      • Obyn also multiplies the cash you would have received of any bloons caught by his Wall of Trees whenever either the Trees get full or you forcibly summon a new Wall of Trees (which will destroy the old one).
  • More Dakka: The Bloons can be a victim of this, as a strategy for many high-grade towers is spamming darts or other projectiles that travel far in all directions and cover as much of the screen as possible.
    • The Dartling Gunner's distinguishing feature is its high fire rate, which can be further amplified by upgrading to Faster Barrel Spin.
    • The Aircraft Carrier's bread and butter is making this via tiny Monkey Aces rapid-firing darts. A Carrier Flagship spawns Aces that spew even more bullets.
    • The Tack Shooter's Blade Maelstrom ability does this by spinning around and spraying sawblades everywhere. In the sixth game, it can be upgraded into a Super Maelstrom that keeps firing for much longer. Additionally, its bottom-path upgrades easily fall into this; Overdrive already shoots incredibly fast, while The Tack Zone creates a huge storm of tacks near itself that covers a massive radius.
    Many, many tacks.
    • If you place lots of 2-0-2 or 2-0-3 Monkey Subs on a map with lots of water, such as Spice Islands, you can make this. 2-0-4 makes the darts do extra damage to MOAB-class bloons too.
    • A top-path Monkey Ace in BTD6 eventually becomes the Sky Shredder, which leaves no part of the screen untouched by its hypersonic rain of darts.
  • Mutually Exclusive Powerups:
    • BTD5 lets you pick two upgrades on each path, and two more on a single path.
    • In BTD6, each tower has three paths, but a tower can only have upgrades from two of them at once. Once you have upgrades in two paths, the third path will be closed. In addition, only one path can go into tier 3 upgrade and beyond, while the other is stuck at tier 2.
  • Nerf: Many, many of the towers and their upgrades, and sometimes even the Bloons themselves, have gotten this as the games and updates passed. The Bloonchipper is probably a notable example of this in BTD Battles. The Ice Monkey and Banana Farm also got hit hard with this in BTD6 compared to how they acted in BTD5. Listing them all would take up an entire subpage.
    • The Ice Monkey's attacks are some of the very few in the fifth generation (i.e. in Bloons TD 5, Bloons Monkey City, and Bloons TD Battles) that could hit infinite amounts of bloons. In the sixth-generation games such as Bloons TD 6, its popping power has been capped at 40-100 individual bloons per shot, depending on the upgrade, severely crippling them.
    • Glaive Ricochet had its popping power reduced from 100 to 40 in between the fifth and sixth generations. This nerf was already in effect in the Flash version of Bloons Monkey City.
    • Perma-Spike shoots its spikes far slower that it previously did after a nerf.
    • Alchemists have been made dramatically less useful in supporting towers that shoot fast due to their buff running out after a certain number of shots. This change alone cascaded and ruined many strategies that relied on this combo.
  • Nintendo Hard:
    • The Hard track in the second game, the Ant Hill track in the fourth game, and Tar Pits and Down the Drain in the fifth game. Some of the daily challenges including "VVVVVV" (August 23, 2014) and "Anti-Camo Dust" (May 17, 2015) are this.
    • If you see a challenge made by the notable users incogneato, sniper355, The Supermonkey (formerly JamesNg2), lla26, Gamzdude, or Superbloons321 (formerly Simone Esposito), you better run for your life. Or alternately, consult the first of the list for a guide through Ninja Kiwi's forums or YouTube.
    • Impoppable difficulty in the mobile and Steam releases can easily be this, especially on harder maps.
    • Mastery mode. Bloons are one rank higher (red=blue, blue=green, etc.), yet you only get non-mastery cash from popping them. Lower difficulties combined with easier maps can still be challenging, but not quite this. Impoppable (and even Hard on later maps) combined with Mastery can be extremely brutal.
    • In BTD6, C.H.I.M.P.S. is no doubt this. To even play it, you have to complete Impoppable, plus its difficulty is absolutely absurd. You can't use any continues and powers, plus Monkey Knowledge and Banana Farms (as well as any tower that generates extra income) don't work on C.H.I.M.P.S., and just like Impoppable, you can't lose a single life. The game even calls it "the true test of a BTD master", which alone says for how difficult it is.
  • Non-Indicative Difficulty:
    • Discussed in one of BTD3's pre-round comments.
      "Some tracks are hard on easy, and others are easy on hard. Ain't life funny."
    • In the fifth game, Tunnels is infamously easy despite its "Expert" rating, because MOAB-class bloons fly over the tunnels instead of through them, so they are not protected by the tunnels unlike regular bloons, and the bloons you can see always travel in perfectly straight lines, perfect to be popped by Dart Monkeys, Ninja Monkeys, Super Monkeys, Glue Gunners, and especially Dartling Gunners.
    • On the other end of the spectrum, Crypt Keeper and Downstream are rated "Advanced", yet their designs reek of an Expert map. Alongside these is the Intermediate map River Rapids, which is considered to be Advanced by a few.
    • Hedges in BTD6 is often considered to be the hardest Beginner map. The Bloons travel up and down multiply twisty paths, most being blocked by hedges. You can't place towers like Druids and Wizards inside the innermost bends, and the line of sight blockers are very intrusive (if you place a tower on the side, half the map is blocked off).
    • Bazaar, also from BTD6, is an Intermediate map. It has two entrances and exits that have a small overlap area, water towers can just barely reach both paths, and there are a lot of line of sight blockers.
    • Cracked is one of the easiest Intermediate maps, consisting of one long, jagged path with plenty of bends, and a small pond of water that's efficiently close to the path.
    • Chutes in BTD6 despite being an Intermediate map is often considered more difficult than some Advanced maps. It consists of two separate, relatively short paths with only one small intersecting area.
    • Cornfield is quite simple and straightforward compared to other Advanced maps like Pat's Pond and X Factor. Its gimmick is that almost the entire map is covered in stalks of corn that need to be cut down before towers can be placed, but often times you'll only need to remove a few, due to BTD6's increased focus on a few synergistic towers rather than spamming. The path has multiple bends, is decently long, and there is only one entrance and exit.
    • Off the Coast seems intimidating with how half the map is covered in water, but it has only a minor and insignificant line of sight blocker. Having so much water lets you use the spamming powers of the Monkey Sub and Admiral Brickell to their maximum potential. It helps that the map only has one path that crosses into both the land and the sea.
    • Dark Castle is rated Expert in-game, but according to most players, it's easier than some Advanced maps like Peninsula, and definitely much easier than its fellow Expert maps QUAD, Muddy Puddles, and #Ouch. The map features four paths that converge into one to enter the castle, but that's not a very big threat.
    • A milder case, but Infernal is known as the second-easiest Expert map, after Dark Castle. The map features two rather long paths, which alternate between rounds. While the severe lack of land can be intimidating at first, global-range towers like Heli Plot will absolutely destroy the map.
    • Geared is an advanced map with only one path, but after every round, all towers you place are rotated around the center of the map by one eight of a turn. This means that if you do not use global ranged towers, you risk having no defense on the rounds where all your good DPS makers are at the bottom. As a result, the early-game is brutally hard, especially on CHIMPS where you cannot afford any global range tower to start with. For this reasons, it's seen as an expert map.
    • Lampshaded in an Odyssey titled "Journey of the Misplaced": the maps are Cracked, Rake, Chutes, Hedge, Dark Castle, and Geared. All ones that are considered easier or harder than their respective difficulties.
  • No Plot? No Problem!: As the entire series was based off a simple flash game where a monkey pops balloons, no real plot has ever been added. Bloons Adventure Time Tower Defense subverts this by having a plot in which the Bloons invade the land of Ooo. It's pretty simple but it's something.
  • No-Sell:
    • Black Bloons are immune to explosives, White Bloons cannot be frozen, Zebra Bloons have both the properties of black and white, Purple Bloons are immune to energy and magic-based attacks, and Lead Bloons cannot be damaged by sharp objects (and Super Monkey/Laser Cannon lasers, but Plasma and the Sun God can, since BTD4). The MOAB and BFB are immune to anything that slows them down, as well as the Super Monkey Storm (in the third and fourth games). The ZOMG will merely take 1000 damage from one of the Bomb Tower's MOAB Assassin ability in BTD5.
    • Super Monkey Storm used to avert this in BTD5, as it used to destroy everything (Including ZOMGs) in one use. However, you only get one use per game! Due to a patch, however, Super Monkey Storms now only do 1000 damage to ZOMGs.
    • The BAD in BTD6 can't even be affected by any of the abilities, excluding those that will instantly damage it.
  • Not Completely Useless: In Bloons TD 6:
    • Lead to Gold is a tier 3 upgrade for the Alchemist that lets it instantly pop lead bloons and turn them into $50 each. While it's a relatively cheap upgrade, lead bloons aren't very common, and there are much more useful ways of popping them. Lead to Gold also works on DDTs, but they move incredibly fast and have camo (which the Alchemist can't detect), so it's not a particularly effective attack against them. However, it did see use in an Odyssey which added many more Leads to the normal rounds.
    • Grand Saboteur, the tier 5 middle path ninja monkey upgrade, sees very little use outside of freeplay rounds due to its poor cost-efficiency. It costs a similar amount to four Bloon Saboteurs, but four saboteurs can permanently slow down bloons by using their sabotage abilities in sequential order as each expires (and even CHIMPS runs on the hardest maps use two saboteurs maximum), yet Grand Sabotage can only apply its effects for half of its own cooldown. Grand Sabotage is especially reviled by 2MPC challengers because its ability to damage all new blimps by 25% can erase many thousands of pops that were supposed to go to the main attacking tower. But in Freeplay, it is very useful due to its Percent Damage Attack being coveted to fight against BADs' eternally increasing health, since BADs cannot be slowed down by any means.
  • Nuke 'em:
    • The Monkey Ace ability Ground Zero. It wipes out any non-MOAB bloon onscreen and deals 350 damage to MOAB-class bloons.
    • Monkey Sub's "First Strike Capability" clearly references a nuclear armed submarine.
  • Numerical Hard:
    • In games prior to BTD6, the difficulty levels just increase the speed of the bloons, the price of the towers, the number of lives you have, and the amount of rounds thatyou have to play through, although there are alternate gamemodes that drastically change gameplay, such as Deflation and Apopolypse. However, in BTD5's Impoppable difficulty, the MOAB-class bloons are stronger, and there are five ZOMGs at level 85.
    • Generally Averted in BTD6. While the main 4 difficulties are still mainly numerical, there are also sub-difficulties to each difficulty that tend to add in even more rule changes or restrictions.
  • Nostalgia Level:
    • Several retro maps appear in BTD5 Deluxe:
      • Ocean Road, a beginner map that first appeared in the Flash version of BTD4. Featuring a long road with many turns and a lake at the bottom-left, near the exit.
      • Military Base, another beginner map; this one first appeared in the Mobile versions of BTD4. Features a road that centers around a helicopter landing pad, with background elements such as a lake, a runway, and a building with satellite dishes.
      • Pool Table, an intermediate map that first appeared in BTD4, like Ocean Road. The bloons enter in both top corners and the bottom-right, circle around a few times, and exit in the top corners and the bottom-left. It is a confusing map due to the overlapping paths.
      • Railway, an expert map that originated as one of the optional "Premium" maps in the Flash version of BTD4. The bloons enter at five points at the top and the tracks they travel on merge into one path that exits at the bottom, surrounded by water on both sides.
    • BTD6 brings back Park Path, a beginner map from 5, now reworked to fit 6's aesthetics. For added bonus, the music playing in this track is the music from 5.
  • Obvious Rule Patch:
    • It was possible to beat BTD1 using only Dart Monkeys and Tack Towers. BTD2 introduced Lead Bloons which could only be popped with Bomb Towers, and with Black Bloons' existence you wouldn't only rely on those either, thus forcing more tower variety and preventing players from abusing the Hypersonic Tack Tower glitch.
    • In BTD6, the Apache Dartship ended up having its price increased in order to stop players from using it to solo Deflation mode on most maps. At one time, it costed $19,500 (Deflation only gives you $20,000 period); however, with discounts from bottom path Villages, it was still barely affordable. The very next update increased its cost to $19,600, just enough to make it too expensive for Deflation, but not enough to hinder any strategy in other modes.
    • A minor price hike of Arcane Spike wizards was used to put a stop to a once-popular strategy of saving up for Arcane Spike to beat round 40 of CHIMPS alone.
    • During the Easter 2019 Egg Collection event, players figured out the best strategy to farm Eggs is to repeatedly play Dark Castle (the easiest of the Expert maps, rewarding the most Eggs) on Deflation mode (a mode that allows player to be away from keyboard). A minor patch in the middle of the event reduces the Egg rewards from beating Deflation mode to be only 20% of other modes. Note, however, that the devs originally intended for Deflation to have much less than the other modes, and simply forgot about it until people started talking about it.
    • Mana Shield (Monkey Knowledge granting a 25 regenerating extra lives) was formerly usable in Impoppable difficulty, where you're supposed to permanently have one life. A later patch nerfed the shield to be disabled there.
  • One-Hit Kill:
    • The Super Monkey storm. Works on everything except for MOAB-class bloons in 3 and 4. In 5, it is played straight, except for ZOMGs.
    • If a MOAB-class bloon slips through your defenses, it will take enough lives to instantly make you lose in any game mode. You can use towers with life gain abilities, but you'll still need to generate several hundred lives to survive.
    • The MOAB Takedown ability in BTD5 will reel in a bloon of any rank up to a BFB. In 6, the Pirate Lord upgrade allows this ability to target up to three blimps at once. It can also spend two hooks to one-shot a ZOMG.
    • The Technological Terror can execute a shockwave powerful enough to practically destroy everything in its radius that isn't a ZOMG.
    • The submarine gets this ability with the First Strike Capability upgrade: a single missile, on an extremely long recharge time, which is extremely notable as it's the only one that can deal enough damage to completely destroy a ZOMG in one hit, leaving no child bloons behind.
    • In BTD6, the Druid of the Jungle can grow vines to ensnare bloons up to Ceramics. It takes time, but any bloon caught in the vines are guaranteed popped, even if it's in a Custom Challenge modified to have 2000% HP Ceramic. It's one of the few "true" one-hit kills in the game.
  • One-Hit Point Wonder: In Impoppable mode (as well as CHIMPS in BTD6), you only have one life, and you cannot get more through either abilities or the Healthy Bananas upgrade. You can't even let a Red bloon leak.
  • One-Hit Polykill: A default ability in almost every tower, given that regular bloons only take 1 hit to kill.
  • Ominous Visual Glitch: If a Bloon is affected with Benjamin's Bloon Trojan in BTD6, glitchy graphics appear on it.
  • Painfully Slow Projectile: The darts fired by Monkey Aces travel super slowly as they travel from the plane to the edges of the map. Even if upgraded to home onto bloons, they're still rather slow.
  • Percent Damage Attack: Ezili's MOAB Hex, the Alchemist's Unstable Concoction, and Grand Saboteur's ability, all introduced in Bloons TD 6. The MOAB Hex ability takes away 4% (or 5% at level 20) of a blimp's HP every second. The Unstable Concoction attack covers blimps with a concoction that creates an explosion when the blimp's current layer is popped. The explosion's damage is worth 10% of the blimp's HP. The Grand Saboteur ability reduces the health of all newly spawned blimps by 20% when the ability is active.
  • Play Every Day: The Daily Challenges in 5 and 6. They can range from outright trivial to nightmarish (see Nintendo Hard above).
  • Power-Up Letdown: Sun Temple / True Sun God insta-monkeys in BTD6. While getting the strongest tower in the game for no money at all sounds downright broken, and it does still shred through early to mid-game rounds effectively, they're completely incapable of taking sacrifices, which locks away a huge amount of their power to the point that Sun Avatar insta-monkeys end up outclassing them in the late game. This also applies to Sun Temple/True Sun God without sacrifices in general. A no-sacrifice Temple isn't that much better (and in some cases actually worse) than a Sun Avatar despite costing 100k cash, while a no-sacrifice True Sun God only offers triple the damage, despite costing around five times of a Temple.
  • Precision F-Strike: Round 14's tip on the Super Monkey. Also round 63 of BTD5, though it later got removed.
  • Precision-Guided Boomerang: Actually averted with the Boomerang monkeys—after being thrown, their boomerangs go in a set circular path, or a straight line out and back if Kylie Boomerangs are bought. Played straight with Glaive Ricochet (3rd upgrade, 1st path), glaives bounce from bloon to bloon.
  • Ptero Soarer: The Radadactyls in BTD5 appear to lack pycnofibers and have batlike wings. And a crest like a Pteranodon's. It's especially prominent in the Pro version.
  • Randomly Generated Quests: BTD5 has a Quests tab in the menu, available by clicking on a monkey wearing a red hat. It shows three quests selected from a pre-determined pool, which typically involve popping a certain number of bloons, using certain towers, or beating maps. Most quests have a duration of one day, but some longer ones last five. After a quest is completed, you're able to collect a reward, which is usually Monkey Money, Special Agents, or free towers.
  • Real Is Brown: BTD4 has a darker and more desaturated artstyle, with monkey designs (for instance, the Boomerang Monkey and the Super Monkey) and certain tracks looking more washed out. This is noticeable when compared to the relatively bright first three games and sequels.
  • Recurring Riff: The Main Theme, which is present in some form in all mainline games from the fourth game onwards. In BTD4, it is the only music that plays throughout the game. In BTD5, all the other themes are remixes of the Main Theme. In BTD6, it's not as present, but if you listen closely to Party Time, the sixth game's title theme, you can hear the bass in the background playing the Main Theme.
  • Regenerating Health: BTD5 gives us Regrow Bloons: Heart-shaped bloons which, if left unpopped, restore themselves to their original color. This can cause a Hydra Problem: As every Regenerating bloon will restore to the original color, if you only pop one layer of a Regenerating bloon that spawns two lesser Regenerating bloons, both will restore to the original color, doubling the amount of bloons you have to pop. Even worse if it was a Regenerating Ceramic bloon, as the 10-HP ceramic layer will also be restored.
  • Remixed Level:
    • Rink Revenge is a remixed, harder version of the beginner levelThe Rink, with two shorter paths instead of one long path.
    • Flooded Lane is Monkey Lane, but almost completely covered in water, making it hard to place a majority of towers.
    • Spooky Castle is the Halloween version of Castle, with similar layout, but different paths. Note that Castle is already an Expert difficulty map.
    • Muddy Puddles is already one of the hardest maps in BTD6, and then Ninja Kiwi released the even harder Bloody Puddles. Muddy Puddles have four short paths with Bloons appearing on one path at a time. Bloody Puddles have five paths and the Bloons appear on two paths at once.
  • Ridiculously Fast Construction: BTD6 has the map High Finance, in which you only have a tiny plot of land to place your towers in at first, but you can also pay to build structures which towers can also stand on, built in only a few sections.
  • RPG Elements: The series has a history of this throughout its towers.
    • For most of the series, you only needed enough money to afford the next upgrade. With BTD4, ranks must be earned to unlock all of the towers and top tier upgrades.
    • In BTD5, however, all upgrades and towers must be unlocked. Both can be unlocked through rank-up, but a tower will need experience in the case of the former. Another case of the former is that rank-up only unlocks the final upgrades of the towers.
    • The Heroes in BTD6 gain EXP and level up as the rounds pass after placing them down, and you can also manually level them up with the in-game cash.
      • On the topic of EXP, your towers will also gain EXP after a round passes if they're placed in the map. You can use this EXP to unlock upgrades for them.
    • BATTD shares the same heroes gimmick as in BTD6 in that you can only place one of them per map, and also adds a few new elements, such as trinkets and weapons the characters can hold.

    S-Z 
  • Sandbox Mode: The games starting from 4 (which was likely the Trope Namer) include a sandbox mode which is unlocked at rank 25/26 in which you have nearly unlimited money and lives and you can test all towers as well as bloons in it.
  • Secret Level: The map "Blons" in BTD6. It can only be played in the Challenge Editor, by clicking "Random" until the map gets selected. Once you've beaten a challenge on the map, it becomes selectable normally on the editor (you still can't play it on normal modes, though).
  • Serial Escalation:
    • In BTD1, the strongest bloons were Black Bloons and White Bloons. In BTD2, the strongest bloon was the Rainbow Bloon, which contained 2 Blacks and 2 Whites. In BTD3 we meet the first real "boss", the MOAB, which is an instant game-over if it leaks and has 4 Ceramic Bloons in it. Each game since then has introduced a progressively higher-ranked blimp—BFB in 4, ZOMG in 5, and BAD in 6.
    • The tower upgrades. In the first two games, each tower only has two simple upgrades, like extra range or attack speed. The third game adds two more upgrades, which are stronger but still simple. The fourth game towers also only have four upgrades each, but also arrange them linearly where the fourth upgrade heavily increases the tower's power. The fifth game doubles the number of upgrades, arranging them into two upgrade paths for each tower. The sixth game has three upgrade paths for each tower, and adds fifth tier upgrades, for a total of 15 upgrades per tower.
    • Think you're good at the game? Can you take on Impoppable with ease? Here comes a new, even more difficult game mode right after it in the sixth game; C.H.I.M.P.S. In short, you can't leak anything (nor can you use a continue to salvage your game should you lose), you can't use any powers, Monkey Knowledge upgrades don't apply, you can't get any extra income (meaning that the Banana Farm is entirely useless in this mode), and to top it all off, you can't sell any of your towers. The game calls it "the true test of a BTD master" for a good reason.
  • Sentry Gun: Some towers, like the Tack Shooter, the Bomb Shooter, and the Spike Factory, seem to be fully autonomous machines that can automatically attack Bloons without any monkeys controlling them. There's also the Engineer's sentries, which also fire automatically at Bloons.
  • Short-Range Shotgun: Buckshot and its upgrades severely reduce the lifetime of Dartling projectiles.
  • Shotguns Are Just Better: The Buckshot path of the Dartling Gun swaps out high fire rate for a burst of high-damage pellets.
  • Shout-Out:
    • Super Monkeys are a blatant reference to several superheroes:
      • Its basic appearance is a reference to Superman, further solidified by its Laser Vision upgrade being incapable of popping Lead Bloons.
      • The Laser Vision and Plasma Vision upgrades give it a visor that bears a resemblance to Cyclops's.
      • The Robo-Monkey upgrade looks like Robocop and its description references the "part man, and part machine" quote.
      • In BTD6, the Dark Knight upgrade makes it a blatant Batman expy, thanks to its name, costume, and shooting blades that vaguely resemble Batarangs. Its following upgrades also follow this trend.
    • In BTD4:
    • In BTD5:
  • Skill Gate Character: In BTD6, the hero Sauda works like this. Her attacking power is extremely high at close range, and she does very well on tracks with criss-crossing or curved paths, which many of the Beginner and several of the Intermediate maps have. However, she doesn't do well on maps with multiple paths or limited land near the track, so her power declines sharply on most of the Advanced and Expert maps.
  • Smart Bomb:
    • In BTD3 and BTD4, the Monkey Beacon can be upgraded to call in the Super Monkey Storm, which insta-kill every single bloon on the screen. Well, except MOAB-class bloons. In BTD5, this same thing appears as a Special Agent, and it wrecks everything but ZOMGs.
    • The Ground Zero ability for the Monkey Ace does this, and takes it quite literally, by dropping a bomb that deals huge damage to all Bloons on screen, enough to wipe out weaker Bloons! The Tsar Bomba in BTD6 drops a bomb that's even larger than Ground Zero, able to take down BFBs and stun ZOMGs!
    • In BTD6, the final bottom path upgrade for the Bomb Shooter, Bomb Blitz, blows up almost all of the Bloons on screen with a series of huge explosions when a life is lost.
  • Snowlems: The Mad Snowman special agent in 5. It's a snowman that throws snowballs at Bloons to pop and freeze them. It also melts away after a certain number of rounds.
  • So Last Season: As bloons get tougher and tougher with each passing game, so do the monkeys. After the game that introduced them, the strongest of bloons become noticeably easier to deal with:
    • Ceramic Bloons in BTD3 and BTD4 could not be slowed down by glue and there were no towers capable of dealing extra damage to them - only the Super Monkey Storm could instantly destroy them. BTD4 made them easier to deal with thanks to the introduction of tower upgrades that can destroy multiple layers in one hit. Finally, from BTD5 onwards, they can be slowed down by glue (not helped by Bloon Dissolver and Bloon Liquefier being capable of eating the Ceramic layer very quickly), and upgrades such as Juggernaut and Deadly Precision could deal extra damage or outright pop it in one shot.
    • The MOAB in BTD3 could not be slowed down by ice or glue, and could not be damaged by Super Monkey Storm. Furthermore, just like Ceramic Bloons, there were no towers capable of dealing more than 1 damage per hit. In BTD4, MOAB Maulers were introduced and could deal 10 times that damage; in BTD5 they were no longer immune to the Super Monkey Storm, and more anti-MOAB measures (including abilities capable of one-shooting a MOAB) were introduced. In BTD6, almost any tier 5 tower can eat them for breakfast, to the point their Ceramic children are more dangerous than them.
    • The BFB in BTD4 was mostly like the MOAB in that it had the same immunities and countermeasures. In BTD5 they can be popped in one hit by Monkey Pirates, Technological Terrors or First Strike Capability, which was expanded into more abilities from other towers as well as ways to slow it down in BTD6.
    • The ZOMG in BTD5 was immune to a lot of tower abilities and it took reduced damage from the ones it was not immune to. Only the First Strike Capability ability could one-shot it before Freeplay. BTD6 introduces more ways to take down a ZOMG in one hit as well as means to stall them down with ice, glue or stuns (albeit with reduced effect compared to MOABs and BFBs, and a ZOMG's Fortified property cannot be removed).
    • In BMC it is impossible to remove a DDT's special traits. The Mortar Tower's Blooncinerator ability in BTD6 can remove its Camo and Fortified traits.
  • Spell My Name with an "S": CHIMPS mode is spelled with periods as "C.H.I.M.P.S." in the debriefing window when you load or create a save file. However it's spelled without periods on the save loading button, the Co-op debriefing window and on the Hard-difficulty mode selection screen.
  • Spike Balls of Doom:
    • The Spike-o-pult (and its upgrades) launches these, with the tower being worked into the Dart Monkey from BTD4 onward. In BTD6, the Spike-o-pult's path's final upgrade, Ultra-Juggernaut, launches a giant spiked balls that split into multiple smaller spiked balls.
    • The Spike Factory can be upgraded to produce these. The next upgrade makes the spike balls Made of Explodium.
  • Spikes of Doom: Road Spikes can be placed on the floor, and will pop 10 or 11 bloons before disappearing. The Spike Factory will periodically place spikes on any section of path in its radius, making less need for road spikes.
  • Splash Damage: Many upgrades give towers this ability, but Mortars and Cannons have it as their bread-and-butter.
  • Splash Damage Abuse: In Bloons Tower Defense 4, Camo bloons can't be targeted by most towers; however, if a tower attacks another bloon and the camo bloon happens to be in the path or blast radius of the attack, it'll still get popped. This is no longer the case in later games, however, where camo bloons completely ignore attacks from most towers that don't have camo detection.
  • Spread Shot: Sun God Monkeys have a rapid piercing 3-way eye beam, while Monkey Buccaneers can be upgraded to have a 5-way shot, the regular dart monkey can have a 3-way shot, and the Dartling Gun can be upgraded into this in the missile line in BTD5, and the Buckshot path in BTD6.
  • Standard Status Effects: While most towers are designed only for destruction, a few specialized abilities are required by some.
    • Ice Towers can freeze bloons in place, and even slow them down permanently with the Permafrost upgrade.
    • Glue Piles (and in later versions Glue Gunners) slow down the fast-moving bloons.
    • Glue Gunners with corrosive glue can also give the bloons an effect similar to poison, while slowing them down at the same time.
    • The Burny Stuff upgrade for mortars set bloons on fire. Other attacks like the Buccaneer's flaming grapes and Gwendolin's flamethrower can also inflict Burn.
    • Alchemists in BTD6 throws acid bottles that eat away several Bloon layers over time as their basic attack.
    • The Bloon Impact upgrade for the Bomb Tower and the Mortar's Pop and Awe ability can stun Bloons, stopping them from moving for a while. Striker Jones can also stun with his level Concussion Shot ability.
  • Stealthy Mook: Camo Bloons. Most towers will not detect them, but there are specialized towers that can, and certain abilities that can allow nearby towers to spot them.
  • Stop Poking Me!: In BTD6 and Bloons Adventure Time TD, hero characters become annoyed after you tap them too many times in a row.
  • Suspicious Video-Game Generosity: Waves right before a Difficulty Spike will tend to through lots of weak bloons at you to give you some cash (notably the wave prior to the first Lead bloons). The text popup in between rounds tends to give some advance warning and in some games even acknowledges that you're getting the cash for a reason.
  • Symbol Swearing: Round 63 for older versions of BTD5: "Next round will be @#$*% hard."
  • Technicolor Toxin: Bloon Dissolver, Bloon Liquefier and Bloon Solver glue are green. Likewise, in BTD6, the acid that splashes out of Alchemists' potions is red, and can be upgraded to purple.
  • Tech Tree:
    • The tower upgrades in BTD5 and BTD6.
      • In 5, each tower now has two upgrade paths that can be chosen from. You can go two upgrades down both paths without penalty, but after you pick a third upgrade from either, you can no longer go beyond the second upgrade from the path you didn't pick.
      • It's taken even further in 6; all towers have three different paths of upgrades, but each tower can only choose two paths before the other one closes. In addition, the same rules from before apply in that a tower can only have one path have a third path or higher, and in addition, only one 5th tier upgrade per tower can be put in per gameplay session.
    • The Monkey Knowledge upgrades in 6, in which they take it to its traditional roots. You need to spend a Knowledge Point to unlock a permanent upgrade for your towers. An upgrade can only be unlocked only if the previous upgrade has also been unlocked as well.
  • Temporary Online Content: In BTD6, October and December 2020 saw the arrival of limited-time holiday-themed Trophy Store items. Thankfully, they were timed so that even if you have no trophies when they first arrive, you'll still be able to earn enough and get them all. Additionally, the October ones were teased with a "start collecting trophies" message in the news a week or two before their arrival.
  • Tempting Fate: The description for the ZOMG in BTD6 when it first comes out is one, possibly foreshadowing the existence of the BAD if you go far enough.
    "Surely this is the largest thing the Bloons could possibly send at us? Right...?"
  • The Tetris Effect: Best to stay away from carnivals and parties after playing this game for too long.
  • There Is No Kill Like Overkill: "Overkill" doesn't seem to be a word in the monkey vocabulary. For context, in order to pop an army of balloons and blimps, a few of the weapons you can choose are Humongous Mecha with antimatter cannons, nuclear warheads, Sun Gods, experimental death rays, missile launchers, armed gunships, rapid-fire 3-barreled rocket machine guns, an orbital strikes, aircraft carriers, giant phoenixes, high-level magic... the list goes on and on.
  • Too Awesome to Use: Insta-Monkeys in BTD6, especially for tier 4 and 5 monkeys. An Insta-Monkey lets you place a pre-upgraded tower for free. High-tier Instas can potentially save you tens or hundreds thousands of cash. On the other hand, login bonuses only give you low-tier ones every few days, and the other way to get them is reaching round 100 in a game. Even then, you'll mostly get Tier 3 ones. Tier 4 Instas are rare, and you'll need to play Expert maps for a decent chance of them. Tier 5 ones are even rarer, only being obtainable through special events, and even then, only with a massive amount of grinding.
  • Turtle Power: The Tribal Turtle, a Special Agent in BTD5, is a turtle who throws spears and coconuts. It's notable for being one of the few amphibious towers in the series.
  • 2½D: Bloons TD 6 uses 3D graphics and modelling, but gameplay logic is still almost entirely 2D, with height only being used to determine a tower's line of sight. This leads to quite a bit of Depth Perplexion instances. A mod that allows you to move the camera shows the discrepancy between the model's positions and the actual, logical positions used in gameplay.
  • Tyop on the Cover: The Double HP MOABs game mode in Bloons TD 6 is capitalized incorrectly as "Double Hp MOABs" in-game, such as on the load game button and the intro message to any Co-op game played on it.
  • Unexpected Shmup Level: The Direct Assault Mission from BTD5 Deluxe. Rather than a winding path, bloons come straight from the right to the left from every height. Your main tools in stopping the onslaught are the manually aimed Dartling Guns.
  • Unwinnable by Design: A gimmick in the Needs Healing odyssey in 6. Each island sends out a camo regrow ceramic (which will take away 104 out of your 105 lives) on the very first round that cannot be killed whole, and you are supposed to restore the lives by various means. On Hard Mode, you cannot reuse healing towers between tracks except for the Hero Unit Benjamin. If you misallocated your towers, powers, and Monkey Knowledge so that you cannot heal sufficient health or use powers to mitigate the damage caused by the initial ceramic on each island, the odyssey is unwinnable and you have to restart it from the beginning.
  • Unwinnable by Mistake:
    • In BTD6, expert maps on CHIMPS are said by Ninja Kiwi themselves are not checked to see if they can be won. Balance changes in patches rarely take the plausibility of expert maps CHIMPS into account. As of patch 23.x, the only map impossible on singleplayer CHIMPS mode was Ravine.
    • Certain Daily Challenges from 5 like Anti-Camo Dust, Highly Opinionated, and Ten Hits were impossible for many players and so they had to be fixed later, either after 12 hours since the challenge released to even three months after they initially expired. A list of impossible DCs can be found here.
    • Bloons TD 6 had the February 1, 2021 Advanced Challenge, "Okampuss's Challenge", that was accidentally made impossible for several hours due to Ninja Kiwi swapping the health bonuses given to ceramics and to blimps. Blimps were supposed to have quadruple health and ceramics should have had normal health. Unfortunately, NK mistakenly quadrupled the health of the ceramics instead and kept the blimp HP as normal, making the ceramics too tough for the lone sniper provided in the challenge to shoot down. Thankfully, the health bonuses were corrected later on in the day.
  • Updated Re-release: Bloons TD5 on Steam, which replaces Deluxe. Even though it seems like a direct port of the tablet versions, there are some changes, such as no IAPs (with the exception of cosmetic changes).
  • Useless Useful Spell:
    • Comanche Defense in Bloons TD 6 gives an ability that summons three Comanche helicopters that last for ten seconds "when they're most needed", but with caveats that nullify this assurance. The extra helicopters only appear when there is 2000 RBE on the screen (note that a MOAB is worth only 616 RBE) and take 25 seconds to recharge, leaving the main Comanche a sitting duck with little popping power other than its MOAB shove skills. The ability automatically triggers when both the recharge and RBE conditions are met even if the player thinks it isn't desirable to send out the extra Comanches at that time.
    • The Legend of the Night's Unrealistic Black Hole attack easily qualifies. The black hole can suck up any leak for 7.5 seconds and kill the leaking bloons in one hit; even the BAD is not immune to it. Unfortunately, its very high price (costing over $200,000 on Easy difficulty) makes it not cost-effective in non-freeplay rounds, and even in freeplay its use is nonexistent because the construction of the Vengeful True Sun God (a powerful tower essential to freeplay runs) permanently disables the Legend of the Night upgrade, leaving the black holes unavailable.
    • Faster Darts, the tier 1 bottom-path helicopter upgrade, increases the projectile speed of the helicopter's darts. It does not increase their rate of fire (which is what the next upgrade, Faster Firing, does). This upgrade does little to nothing for the helicopter since its attacking style (especially for higher tiers) is primarily based on hounding bloons at close range.
    • In Impoppable and CHIMPS, Ezili's Sacrificial Totem ability, which grants multiple status buffs and camo detection to affected towers, becomes this. It is disabled if you lack enough lives to sacrifice to it, and both those modes leave you as a One-Hit Point Wonder and disable all means of gaining extra lives.
    • The bottom-path Wizard Monkey upgrade Soulbind was very quickly reworked from scratch into Prince of Darkness precisely because the soulbinding ability was the game's purest example of this trope. You could bind towers with an ability that would sell the towers and convert one hundredth of the tower's cost into lives. Sounds cool, doesn't it? But this was an absolutely terrible bargain: a tower costing around $10,000 would only give approximately 100 lives, all of which could be destroyed by a single ceramic or blimp (which were everywhere from the midgame onwards). Needless to say, sacrificing towers (that could have hindered the leaks in the first place) for a pittance of lives proved to be completely useless.
    • The tier 4 Ice Monkey upgrades in Bloons TD 5 were considered the most useless tier 4 upgrades in the fifth generation games, and for good reason.
      • Viral Frost did not come back for Bloons TD 6 due to its sheer uselessness of its own attacks. It was supposed to allow bloons frozen by the Viral Frost to freeze other bloons coming into contact with them, even if the unlucky bloons were outside the range of the Ice Monkey itself, or were camo, white or zebras (all normally immune to freeze attacks). But an Arctic Wind (the predecessor upgrade to Viral Frost) could destroy all non-blimp bloons with only the assistance of a Monkey Intelligence Bureau in the Flash games, making the viral frost effect completely worthless. Viral Frost's only useful purpose was to be a temple sacrifice.
      • Absolute Zero's fifth-generation Flash version also qualified as a Useless Useful Spell. It froze bloons across the whole screen for four seconds, and affected camo bloons as well. Sadly, the Flash version did not allow it to freeze blimps, making it obsolete very fast. Even worse, frozen bloons would No-Sell several towers and upgrades, and thus freezing all bloons on screen lowered their overall damage to the rush. Finally, the frost effect wears off if the now-frozen bloons are popped. In every way Absolute Zero was outclassed by the similar-cost Sabotage Supply Lines. The mobile-derived versions made Absolute Zero less useless by allowing the ability to slow down blimps (stacking on top of sabotage), and Bloons TD 6 gave its counterpart's ability (Snowstorm) the power to briefly slow down blimps significantly.
    • Bloons TD 4 onwards give the Monkey Ace an upgrade that drops exploding pineapplesnote , which gave the Ace a useful explosive that when spammed, could carpet bomb an entire map. Unfortunately, 5 onwards nerfed it to the ground by severely slowing down the pineapples' attack rate, and they often explode in all sorts of random and useless locations where no bloons are. They only do 1 damage, to boot.
    • Bloon Master Alchemist and Benjamin are massive liabilities in CHIMPS, due to them both being towers dedicated to both earning income and bypassing entire bloon layers at once. Income generation is disabled in CHIMPS and their blimp-targeted bloon layer bypasses deny you a lot of the bloon pop income you would have received had you popped the blimps with brute force.
    • Striker Jones's level 10 ability, Artillery Command, is an example of this trope until its level 20 upgrade. It resets the cooldowns of all Mortar Monkey and Bomb Tower abilities, and itself has a very long cooldown. The problem? Only three abilities in the entire game fit this bill: the MOAB Assassin, MOAB Eliminator, and Pop and Awe abilities. All three of them are considered not very cost-effective, and the MOAB Eliminator has an extremely fast cooldown regardless. The level 20 version averts the trope as it gains a much more useful function of doubling the damage and pierce of Bomb Towers and Mortars for 10 seconds.
  • Vagueness Is Coming:
    • BTD5 doesn't tell you what round 85 will bring until it's actually started for the first time.
    If you're playing on Hard, you've done well to get this far, but it will all end next level.
    • The majority of the 5th tier upgrades in BTD6 are pretty vague, not really describing much about what the upgrade does, other than the fact that it's immensely powerful.
    Flying Fortress: This is a BIG plane.
    • The Monkey Knowledge upgrade "There Can Be Only One" shows an image of the True Sun God. Its description is the same thing as its name, so what does it actually do? It combines itself with both the Anti-Bloon and Legend of the Night together via sacrificing them if you have all three 5th tier Super Monkeys on the map, and that they weren't already sacrificed when the True Sun God was put on the map.
  • Video Game 3D Leap: The sixth game has towers rendered in 3D, and even that obstruct their vision, although many 2D-reliant conventions remain, such as spikes placed on the ground still managing to hit bloons flying as high as blimps.
  • Videogame Flamethrowers Suck: Averted with the "Dragon's Breath" upgrade for the Monkey Apprentice, which does massive amounts of damage per second and makes for a great defense when saving up money. The hero Gwendolin in 6 uses a flamethrower, and its fast attack speed, high damage, and ability to set Bloons on fire makes her one of the more powerful heroes for offense.
  • Wake-Up Call Boss: The first appearance of Lead, Ceramic, and especially the first MOAB.
  • Wave-Motion Gun: The Ray of Doom, Bloonsday Device, and (arguably) the Sun God and Temple of the Monkey God.
  • Weapon of Mass Destruction:
    • The Temple of the Monkey God is one the most extreme weapons one could ever see. It sacrifices all towers in its former radius when upgrade, but also gets their powers. In fact, when given the max sacrifices, can destroy any bloons that come its way, including ZOMGs and BADs.
    • The Temple of the Monkey God pales in comparison to the Temple of the Vengeful Monkey ability, the Tier 4 Super Monkey Lair upgrade. When activated, it replaces the aforementioned tower... with a darker-colored temple that fires twice the beams, each one being stronger and having more range than that of the regular Temple of the Monkey God. At this point, the damage output all but makes ZOMGs vanish once they approach a maxed Temple's firing range, and even then those blimps are going to need a large speed increase and a huge group to even hope to break through the Temple's "Instant Death" Radius.
    • The Technological Terror is less powerful then a near max temple, but still pretty darn effective. It fires 2 streams of green plasma (each one being piercing more bloons than the regular purple plasma) and has a lethal ability called the "Bloon Annihilation", which generates a short ranged force-field that does 1000 damage to all MOAB-class bloons next to it. Its final upgrade in the 6th game, called "Anti-Bloon", is twice as powerful and has a much stronger ability.
    • There is also the Ray of Doom, which shoots a constant solid beam of bloon destruction with a pop rate of 100, practically killing any and all regular bloons in less then a second. The problem though, is that it is notoriously weak against MOAB-class bloons, since it only pops 1 per frame for those. Even so, a single one is still pretty effective against the MOABs and BFBs. The ZOMGs are another story...
    • The alternate option competing with the Ray of Doom, the Bloon Area Denial System, which fires 3 dart-tipped rockets that do splash damage and can kill any type of Bloon every shot, it's an Dartling gun upgade and keeps all the rate of fire and upgrades to said rate of fire. Oh, and it has a special ability, namely firing a rocket at the 100 closest bloons and repeating for 5 times. This is probably as many rockets as filing the entire screen with rocket turrets can barf out.
    • Both final upgrades for the Monkey Ace: the Spectre which rapidly fires darts and hydra rockets directly at the bloons and the Operation Ground Zero, which grants the ability that can be used to clear the screen of bloons.
    • The Spiked Mines Factory in BTD5: It fires at an extreme rate and its spiked balls explode when they reach their pop cap of 16 bloons. Since its downgrade is the Spiked Ball Factory, its spikes also deal 3 times as much damage to ceramics and MOAB-classers as regular spikes.
    • The Apache Dartship fires darts at the bloons like a machine gun and also fires a quad-storm of rockets every couple of seconds. Its downgrade also allows it to pop bloons with the blades that it uses to fly with.
    • The Bloonsday Device, which has the ability to activate the powerful beam from a satelitte which soars high above the maps. Its pro variation is even more epic, because its beam leaves energy tacks in its wake.
    • The Aircraft Carrier launches up to 3 mini-aces at a time. These mini-aces fire 2 streams of darts and the Monkey Aces trademark 8-dart spread fire. They are great at popping bloons from all around the track.
  • Weapons That Suck: Debuting in Deluxe and reappearing in the mobile and Steam versions of BTD5note , one of the new weapons is the Bloonchipper. It doesn't do damage very quickly, but it can keep a number of bloons permanently busy; even if they survive the first trip through, its vacuum will just lock on to them again before they resume normal travel (provided your other towers don't pop them as soon as they're viable targets). In addition, while it can't normally attack MOAB-class bloons, the final tier upgrade on its first path ultimately lets it chew on them.
  • Weapon of X-Slaying: Many towers have upgrades that specialize in doing bonus damage to certain bloon types, such as (most commonly) MOAB-class bloons, ceramic bloons, or fortified bloons as a whole.
  • Wood Chipper of Doom: Introduced in the fifth game is the Bloonchipper, a mechanical device that sucks in Bloons, shreds them, and spits out the remains, which then can be sucked in again. Its upgrades allow it to suck in more Bloons or shred them faster, and the final upgrade allows it to suck in MOAB-class Bloons, stalling and delaying their movement.
  • You Are Already Dead: Corrosive Glue or higher acids, on anything below a MOAB. The Bloon Liquefier will murder anything ceramic or weaker if it gets its glue on them.
  • You Have Researched Breathing:
    • One of the Alchemist's low tier upgrades is Acid Pool, AKA throwing the acid on the track. Making it egregious, it's one of the more expensive low tier upgrades. Apparently, it's easier for the Alchemist to learn making stronger acid than it is to learn how to throw a bottle on the floor.
    • The Monkey Submarine needs to be upgraded before it can submerge itself in water. It's only available in one upgrade path, too, so other Subs can never submerge themselves.
    • Gwendolin uses a flamethrower as her weapon. She needs to be level 5 before her flames can set the Bloons on fire.
    • The Heli Pilot requires a specific upgrade, the Razor Rotors, before anything takes damage from getting stuck in its fast-moving rotors.
  • You Will Not Evade Me: The Ice Tower's Arctic Wind slows down the bloons, allowing the Snap Freeze effect to pop them down to the last layer (or until it reaches a freezing-immune layer).
  • Zerg Rush: The entire methodology of the Bloon hordes; each higher grade bloon contains so many of the next class down. Sending a whole bunch at one time is what amounts to difficulty in the series.

 
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Alternative Title(s): Bloons TD

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Apache Dartship/Apache Prime

Apache Dartship is the Tier 4 upgrade of Heli Pilot. It adds some missile launchers and a machine gun in addition to the basic darts. Apache Prime is the Tier 5 upgrade, upgrading the darts to lasers, the machine gun to plasma, and the missiles to deal extra damage to MOAB classes.

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