Video Game / Metal Slug Defense

Metal Slug Defense is a mobile game released rather suddenly by SNK in 2014. Despite the title, it is not quite a Tower Defense, but rather a strategy game set in the Metal Slug universe. Players spend a constantly filling meter on various characters and enemies from the series, which then march forward in hopes of overwhelming and destroying the opposite base. The many different human, machine and monster units have a basic attack, as well as unique charged moves which sometimes require good timing to be used correctly.

The game can be played online with friends or random people. As it is a free-to-play game, there are elements such as layers of level grinding, missions costing credits that recharge over time and most of the unlockable characters only being available through a secondary currency more accessible for those willing to spend money on it.

However, all updates to Metal Slug Defense have stopped since late 2015, though this doesn't mean the game services have been discontinued as its still playable to this day, either offline or online. However still, that's planned to be changed as the mobile version will end service on Monday, April 17, 2023. Fortunately, the game will still be playable on PC via Steam.

A sequel by the name of Metal Slug Attack had since been released in February 2016, which vastly improves over MSD in certain aspects and saw constant updates. However, that game's service has ended on Thursday, January 12, 2023.

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Tropes:

• Action Bomb: The Zombie Rebel Soldier, Mutated Soldier, and the Hopper Mecha units self-destruct upon reaching a target. Meanwhile, the Special Force (Rider) needs to rev up his bike before he can crash into an enemy and deal some damage. The player can also release an explosive SV 001 once the "Metal Slug Attack" meter is filled.
• Adaptational Wimp: The four protagonists of the original team of pretty weak in this game.
• Actually Four Mooks: The Hover Unit is deployed in groups of three to justify their high AP cost.
• Advancing Boss of Doom:
  • Every enemy is moving towards the player's base, after all. Even ones such as Jupiter King, who originally moved away.
  • The Huge Hermit - who is the only enemy on its mission - even instakills anything it hits, no matter how much health the target has…except the Stone Turtle, which can even block it.
  • The Stone Turtle, whose regular attack consists of stomping the unit in front of it for huge damage, but moves very slowly towards the other side. It also has a huge amount of health.
  • Rugal Bernstein as a boss (actually the SNK Boss) in Black Noah Attack event starts off with a hyper armor which its impossible to knock him back and he can reach your base in just 5 seconds if don't act quick. Good luck and make sure you have better units because this guy has chunks of HP and his attacks are already deadly as it is.
  • In the Missions tab, you get to fight Big Shiee (the boss from Metal Slug 2/X, Mission 3).
• Airborne Mook:
  • Several of them. Of note is that some can only attack once (or a few times) before leaving the battlefield, but can fly over most enemy forces without being attacked. However, later updates include air units that don't leave the map after attacking, making them quite a threat.
  • The Smasher is normally a grounded unit, but it begins to fly before it attacks with a Ground Pound.
  • Hunter Walkers are normally grounded units, but its special ability allows it to Ceiling Cling and start dropping eyeball bombs in a manner similar to General Morden's Hi-Do special, though the bomb can be blocked from hitting the base if it hits a large unit.
• Allegedly Free Game: The existence of premium currency (Medals) and an energy system (Sortie Points) mean that those who are willing to cough up enough money will always have an advantage over free players.
• Always Accurate Attack:
  • Tetsuyuki sometimes fires a laser that hits the entire field, player base included.
  • Morden's special is to summon the Hi-Do to drop bombs everywhere. The Hi-Do cannot be damaged at all, and it will drop at least one bomb on the enemy base, making it guaranteed to do damage.
• Announcer Chatter: The announcer does his thing when the main characters use their special attack, such as Marco using the HEAVY MACHINE GUN or Fio using the ROCKET LAUNCHER, for example.
• Anti-Air: Certain units have attacks that either shoot projectiles in an arc or at a high angle, allowing them to damage aerial units. The most notable example is the Ptolemaic "Gunnner Unit" (sic), whose special attack sprays bullets in a wide angle.
• Anti Poop-Socking: Missions cost a certain amount of Sortie points which recharge over time. It actually isn't too troublesome after you expand the Sortie point limit to over 400... Unless you're playing the latter levels over and over to get prisoners.
• Art Shift: Ralf, Clark, and Leona use their sprites from the Metal Slug games (which are re-edits of Marco, Tarma, and Eri respectively), while the rest of the King of Fighters cast have a redrawn rendition of their fighting sprites.
• Ascended Extra:
  • Sandbags, usually used by grenade-wielders of the Rebel Army for protection, are an essential tool for survival in this game.
  • The Rebel Army's own soldiers (who usually don't last very long) can prove to be surprisingly effective units if properly used or upgraded.
• Asteroids Monster: The Man Eater plant's special attack is to turn into two seeds that spawn little man eaters.
• Attack! Attack! Attack!: All units will advance forward and exchange fire with enemies until they are killed.
• Awesome, but Impractical:
  • Zombie Marco's powerful and far-reaching blood vomit jet takes a long time to charge up, especially after being used once. Meanwhile he fights with a gun much weaker than normal Marco's and gets face-to-face with enemies despite being a gun user. And upon being hit enough to be knocked down, he takes far too long to stand up.
  • Morden may have a great special attack, but his standard attack is not as effective as his 950 (1500 in Attack) AP cost would lead you to believe and he tends to get knocked back often, leaving the rest of your units exposed as he tries to make his way back to the front.
  • The Commander. His ability to summon Hover Units (and reset that cooldown) seems very awesome, until you find out that said Hover Units give the opponent a pretty good amount of AP if destroyed, making the Commander more of a liability than an asset.
• Big Bad: Morden actually fights on an alien tank without being betrayed this time. The Mars People receive more focus in the last set of bonus levels. While not much of the Amadeus Syndicate is seen in the game, an expansion later added a bunch of units and some levels from the Ptolemaic Army, and later some units from the Invaders too.
• Big Creepy-Crawlies: The Maggot, Snail, Huge Locust and Giant Caterpillar units.
• Bigfoot, Sasquatch, and Yeti: The Sasquatch is one of the better close-range characters due to its speed and high stats.
• "Blind Idiot" Translation: Let's just say that English is not the first language of whomever is doing the translation for the unit descriptions. It's thankfully not a Translation Train Wreck, but it just barely gets the point across at times.
• Bonus Dungeon:
  • At certain hours, a harder set of missions becomes available for 60 minutes. A 100% clear set will become permanently available, setting the next one to appear later. There are twelve total: 4 for Worlds 1, 2, and 3.
  • The Extra World has 9 standard high-sortie-point locations, with the special mission cycling through each day of the week. Note that most of these missions qualify as Harder Than Hard.
  • Mission Mode itself is a gallery of levels with 1 of 2 set conditions (destroy enemy base in X seconds or survive enemy waves for X seconds) designed to showcase the Medal-unlockable units, but it gets surprisingly difficult quite fast (in combination due to the given difficulty level and figuring out the trick for each unit).
• Boring, but Practical:
  • The Rebel Rifleman has a bit less HP than the basic soldier, but is still cheap at 60 AP and shoots from afar while protected by tougher units. The Bikers cost 90 AP but have 1000 HP at level 20 and move faster, while otherwise acting just like the riflemen and complementing them well.
  • The Iron Iso is a stationary tank-turned-artillery-turret that fires long-range piercing shells. That's all it does, but you'd be surprised how much it can accomplish if you keep building them in the same area.
  • The sandbag during early-game. It doesn't attack and serves to protect, but it can stop a Metal Slug Attack and take a good amount of damage during the early game, enough for you to improve your AP regeneration or amass enough AP for a good amount of units.
• Boss Arena Urgency: The Huge Hermit crushes the bridge on its way to the player.
• Boss Battle: Some bosses from the first trilogy such as Shoe & Karn, Iron Nokana and Monoeye show up in certain levels, usually spawning when your units get close to the enemy base.
  • It is also possible to purchase some of these units in the shop, and thus deploy them in missions.
• Bottomless Magazines: In a moment of weakness, units only reload their weapons after using a special attack.
• Bribing Your Way to Victory: Silver Medals can be used to buy items that grant advantages in the missions, such as beginning with full AP regeneration, getting more money after clearing a mission or even unlocking all missions at once. Most units can only be bought with Silver Medals, too.
• The Bus Came Back: Enemies and characters that showed up in one game return for this game.
• The Cameo: Every heroic character from the series is at least mentioned in the game, even those from the Mission and Advance spin-offs, the Ikari Warriors (including Whip and Heidern), the rest of The King of Fighters '94/'95 cast, and even the other mobile spin-off titles. The villain side doesn't get such attention, though recent updates have been trying to rectify that with new units and extra missions.
• Cap:
  • The level cap for units and the player base's attributes is normally 10, but it expands to 20 once the second world is unlocked, and then the base upgrades cap at 30 once the third world is unlocked. The unit level cap, on the other hand, can only be upgraded to 25 by using Silver Medals. Later updates increased the level cap for units further and the posibility to use MSP to increase said cap up to 35. During gameplay, AP recharge speed can be improved 10 times and there is also a limit to how many units can be sent at once.
• Cast of Expies: Many of the Original Generation characters are either an Expy of a character from another work or have a Shout-Out to another work in their design. Details are in the character sheets.
• Charged Attack: Most units can use a special move by spending a meter that fills over time. Oddly, few CPU characters use their special move until the player gets to World 3.
• Christmas Episode: The December events in both games. Appropriately, these also have Christmas themed versions of Eri and Fio, whose weapons are stronger due to their anger from being sent out during their holidays.
• The Computer Is a Cheating Bastard:
  • For some reason, the CPU doesn't use special moves until World 3 but it does work by its own rules in regards to unit creation. It spawns powerful high-cost units from out of nowhere once you get close or hit its base.
  • The difficulty of World 3 mostly comes from the enemy units actually using their special attacks whenever possible, on top of the CPU instantly spawning units at certain conditions.
• Counter-Attack: The scientist zombies don't normally attack, but when they are knocked back (which is almost every time they get hit), they gain a brief moment of invincibility before they launch a powerful short-ranged projectile.
• Death from Above: The Parachute Truck. It fires a bunch of bombs into the air that rain down and pierce enemies until they hit the ground.
• Defeat Means Playable: Clearing a set of levels usually means unlocking the enemies featured in them... to be bought at the shop. The ones unlocked by collecting certain sets of prisoners or getting login bonuses are granted for immediate use, though. Tetsuyuki, Dragon Nosuke and Huge Hermit are unplayable due to being overpowered living bases. The trains from the subway levels can't be unlocked, either.
• Dual Boss: Some missions like to spawn large enemies such as Shoe and Karn or all three Ohumein-Conga at once at some point.
• Elite Mook:
  • The Ptolemaic army units are this compared to their Rebel army counterparts, with their higher HP and the AP cost to go with it, though they do have different methods of attacking.
  • The Future rebel is this compared to every soldier. Even their most basic infantry have 1000 HP at level one.
• Engrish: It's practically a SNK trademark.
• Everything's Deader with Zombies:
  • The zombie enemies from Metal Slug 3 are present. This includes Zombie Marco, who can vomit a danguerous jet of blood.
  • The artwork for World 3 are the same artwork from the previous worlds, edited to make the characters look like zombies. This includes the Mars People for some reason.
• Everything Fades: Dead units may fade, melt or explode.
• Evil Laugh: Allen frequently laughs while attacking. Morden only laughs in his victory pose or if he uses his special.
• Evolving Title Screen: Clearing World 1 makes Satiko Suzuki (the grieving woman) appear on the title screen. Clearing World 2 makes a UFO fly by in the background. Clearing World 3 adds destroyed tanks to the lower-right side.
• Excuse Plot: Morden and the martians are up to no good, so send waves of units at their bases.
• Extended Gameplay: Clearing the game once unlocks a harder loop. It is more of the same in the old arenas with leveled-up enemies, but some missions can surprise the player with an out-of-place boss such as Allen. Later updates added more levels and units, as well as an mode that gives you pre-made unit decks to overcome certain situations.
• Failed a Spot Check: All units refuse to acknowledge the existence of aerial units, even when they are also aerial units. Slow-moving air units like the Hover Vehicle depend on this AI quirk to survive.
• Flavor Text: Each unit has a description about who they are and what they do.
• Final Boss: The final set of boss enemies at Final-5 in World 3 are Iron Nokana+Cyborg Allen O'Neil and then Morden+Jupiter King, supported by hordes of zombie alien clones of Fio.
• Gatling Good: Units such as Marco, some Slugs and Allen wield this weapon either normally or as their special attack.
• Glass Cannon:
  • The HP of the player's base isn't such an important stat to upgrade first because if a decent group of units reaches a base at all, it will most likely be done for because defending units won't have time to charge their special moves to do useful damage and can't even cover their base's hitbox.
  • Tarma's shotgun is powerful, but he needs to get close to enemies for it to hit and if he does use it, his 720 max HP won't keep him alive for a second shot.
  • The Commander is rather fragile for a 210 AP unit, but that's because his main attack is summoning a squad of Hover Units. His special is only a single pistol shot... which resets the cooldown of his main attack, allowing him to deploy more Hover Units faster.
  • Patrol Robots. They don't have much health for a 160 cost unit, but their laser attack has very long range, deals continuous damage that can really add up, and also pushes back enemies very well. They're pretty slow too, however, so you'll need to defend them with more durable units.
  • Utan. For an early-game Zerg Rush unit, this little monkey dies very quickly, but he has very long range (enough to avoid a Scientist Zombie's counterattack), deals good damage, and his special charges quickly and deals good burst damage.
• Going Through the Motions: Characters don't have unique sprites for the cutscenes, only using their animations when idle or out in the field.
• The Goomba: The basic blue soldier you start with. Cheap and with 400 HP at level 20. He attacks at close range with a knife and can throw grenades. The green normal rebel soldier is an unlockable and he has even less health (360 at level 20) for an even lower price.
• Guest Fighter:
  • The collaboration event brings the titular cats from The Battle Cats into the game. Explained as an accident where Morden attempts to summon the Kraken from Metal Slug 7 via his time travel portal and brings in the cats instead. Needless to say, the fans were more than displeased.
  • The entire of The King of Fighters '94 plus Whip were added to a new sixth faction.
• Harder Than Hard: There are three difficulty levels beyond Hard: Very Hard, Expert, and Hell.
• Hitbox Dissonance:
  • The hitbox for the bases is a bit taller than the base itself and some explosions hit farther than they should. The man that sets up barriers will flee whenever a projectile happens to fly above him, as if he was hit.
  • The Claw Unit's special attack has a taller hitbox than what its attack animation would suggest, allowing it to hit high-flying units like the Flying Tara.
• Humongous Mecha: Jupiter King from Metal Slug 3 first appears in area 10, stage 4. The Mars Mecha is also present in the last set of bonus levels. The Gigant Units may also count, its interesting that this units are huge when you check it on your deck.
• Idle Animation: The status screen for the units are where you get to see them standing still. Amusingly, rather than going through a standing animation and then a special one before looping over like everyone else, Marco is completely asleep.
• Immune to Flinching: A select few have this valuable trait, and most of them are great meatshields. Oddly enough, the Rebel Biker does not flinch despite having low HP commonly found among infantry units, and in an interesting twist, the shielded soldiers have such low flinch resistance that they get knocked back on every hit, but their knockback duration is so low that they might as well be immune to knockback anyway.
• Infinity +1 Sword:
  • The Mars People are unlocked on the last level set. They spam laser bubbles at a safe distance (and can fire from above by warping), cost only 80 AP and are produced very quickly. They do need a meat shield to compensate for the slowness of their bubbles, however.
  • By logging on the game every day, you'll eventually get the Elephant Slug, which has plenty of HP and a fireball attack with great reach.
  • Some of the units you unlock from the extra stages are more powerful than most of the other units from the main stages. In particular, extra set 1 gets you the Big Snail and the Giant Caterpillar, two of the best defensive units in the game, while beating extra set 2 unlocks the Samurai Tank, a cheap, long-range unit with a disproportionately high amount of HP.
  • Currently, the best unit is still arguably the Jupiter King, a high-cost, long-range support unit that deals a huge chunk of damage to all enemies in a wide area in one burst. However, the scientist zombies are quickly becoming popular as they are capable of stopping early-game rushes cold and are just generally annoying to get rid of.
• Insurmountable Waist-Height Fence: Sandbags block enemy advances until they're destroyed. In normal Metal Slug games, people would just jump over them instead.
• Kamehame Hadouken: Hyakutaro can fire energy balls from his hands.
• Knockback: Most units suffer from this upon being hit by powerful attacks but surviving. This is important as knockback cancels out attacks that have already been started and gives invincibility frames for the duration of the knockback.
• Know When to Fold 'Em: Abul Abbas waves a white flag and disappears when out of HP.
• Lightning Bruiser:
  • The Natives, introduced in version 1.4.0, are cheap, yet beefy infantry units that have a fast speed and a very fast production speed. Their standard attack is above average for an infantry unit while their special attack has a ridiculous range and deals even more damage. All of this combines into a very effective shock trooper.
  • The Green Hazmat Soldier runs as fast as Natives and has more health than most tanks, with their attacks consisting of a powerful grenade that can destroy air units and a ludicrously powerful bomb that deals huge damage to enemy units and then spawns a similarly tough (but very slow) Mummy. The current meta in Multiplayer consists of rolling out a single one of these guys to stall for time so you can build more powerful units early.
  • Claw units are deceptively slow, but at long range they charge into the fray to maul any enemy in its way. They also have a decent production speed and a good amount of HP.
    • Iori Yagami, who was released as part of SNK's 20th KOF anniversary, will rush at enemies at long range before performing a 3-hit combo on them. Also applies to Vice and Mature, who both rush at enemies when attacking at long range.
• Limit Break:
  • Nearly every unit has a meter that slowly depletes to zero. Once it reaches zero, they can use their Special Attack.
  • A self-destructing SV 001 can be sent when its meter fills. It insta-kills a good number of small enemies before exploding upon colliding with a larger enemy or the opposing base. This is important when fighting Jupiter King, which makes such a mess out of anything you send at it that, at least early on, you're forced to just buy time and try to get rid of large enemies until the bombastic SV 001 is available for damaging and pushing King away.
• Luckily, My Shield Will Protect Me:
  • Shielded Soldiers, who have higher HP than their fellow rebels. Their special move is to make a pushing motion, which blocks all damage. Snails, too, can hide in their shells. Some missions require you to use their defense at the right times to win.
  • Iron Claws and Melty Honeys are tanks with abative shields on the front. With Spikes of Doom to boot.
• Macross Missile Massacre:
  • Several units are able to fire many rocket/missile projectiles. Have a number of them on the screen and you get this trope.
• Made of Iron:
  • For obvious reasons, Allen O'Neil, a barechested soldier, has HP comparable to that of a heavy tank.
  • Instead of dying like other pilots, when the Protogunner is destroyed, Ralf dismounts it and continues the fight on foot. He's just that tough.
  • Most of the human units, compared to their source games. They're no longer One Hit Point Wonders and some can take a fair bit of damage before keeling over.
• Made of Plasticine: Most mook units in general, but the Hazmat Soldier just unceremoniously falls to pieces instead of keeling over.
• Man on Fire: Some units have a burned animation for when they're killed by one of the few fire attacks available.
• Mecha: The Slugnoid, the LV Armor and the Slug Gunner.
• Megaton Punch:
  • Ralf has the notorious Galactica Phantom punch as his special attack.
  • Gunnner (sic) Units have a powerful punch as their standard attack. The Claw Units use a one-two claw punch at close range.
• Mighty Glacier:
  • Units that are slow to produce and slow to move, but pack a hefty punch given their AP cost. This includes...
  • The two variants of Iron Nokana: very slow production speed, but fires bursts of 3 piercing shells, and depending on which version of Iron Nokana you use, can either use a flamethrower to quickly demolish units that come too close or launch a large salvo of long-range missiles.
  • With the Ring Laser Mecha's AP cost reduced to 100, they've become semi-cheap walls that can wipe away most infantry and deal serious damage to other swarming units.
  • The Stone Turtle has an attack that is highly damaging, but its walking speed is very slow.
• Mook Maker: Mummy Generators, Crab Nests and 3-Ton Utility Trucks are obstacles that generate units. Also, Abul Abbas's special ability is to summon a Utility Truck.
• Mundane Utility: Aside from being able to easily murder lesser infantry, the Metal Slug Attack can also be used to destroy enemy projectiles.
• Nerf:
  • The Big Snail used to be a great early-game unit when it was first introduced, having high HP and a devastating short-ranged standard attack that could destroy many other early-game units before they could attack or deliver their full potential. Now its AP cost has been increased and its production speed lowered to discourage snail rushes.
  • The Patrol Robot used to have even longer range, allowing it to harass and knock back units from afar behind the safety of frontal units. Its range has been nerfed by quite a good bit, however, its AP cost has been lowered.
  • When the Parachute Truck was first released, it dropped a hail of projectiles at a good range that did penetrating damage as long as they touched an opponent, decimating even the biggest units in seconds. It got so bad that the following update nerfed them greatly, giving them less range, giving them a longer time to build, and making their attacks no longer penetrate.
• No Fair Cheating:
  • Trying to cheat by using any explicit tools that allows to cheat the game such as increasing the number of medals and sorties, the development team will make your account get suspended and cannot be recovered again once if you get caught doing this behavior which can be found in the rules.
• Non-Lethal Bottomless Pits: You can see this trope by having Ralf use the Galactica Phantom to fall off Giant Hermit's bridge while the Hermit is knocked some steps away.
• Nostalgia Level: All arenas are taken from the series' levels. There often is some continuity between them - you can see a piece of the next level just around the corner.
• Oh, Crap!: If a Miner gets hit before setting a barrier or stationary unit, he freaks out and flees. Rumi is also shown panicking in her icon if a mission is lost. If a defeated unit has a P.O.W. helping, then he goes off running while leaving the rest to die.
• One-Hit Polykill: Some units, like the Ring Laser Mecha, have attacks that can hit any number of enemy units within its range. This is good for dealing damage to important targets that are protected by heavier units, or for clearing away hordes of cannon-fodder units.
• Original Generation: Eris makes her first appearance in Defense in the Relief Supplies Menu and the POW List. She hosts the Build Up section in Attack and gives her very own sprites.
• Palette Swap: Issenmantaro serves as this for Hyakutaro, but more focused on close-quarters combat. The Elite Arabian Soldier serves as this for Abul Abbas; in Defense, the Elite Arabian Soldier has his special attack changed to a charging strike. The Jupiter King MKII serves this as well for the original with its laser attack being replaced to missile.
• "Pop!" Goes the Human: The fat versions of the main characters and Chang's defeat animation.
• Promoted to Playable: Almost everything, from the regular mook to those badass bosses although some units like the Big Shiee will stay as a boss and will not be playable until several updates later. In Attack some units from Defense like the Subway unit that were never playable becomes playable and becomes present in online game play.
• Randomly Drops:
  • Upgrades are unlocked upon rescuing sets of prisoners, but the prisoners aren't seen in the levels and seem to be saved at random upon finishing a mission, to force replays. It's especially annoying in regards to the harder, expensive missions and the bonus ones that are only available for a short time on each day. Of course, you can use silver medals to buy items that guarantee that one prisoner will appear.
  • Completing the extra stages sometimes awards you with a powerup. How it works is not yet determined.
  • With the 1.5.0 update, random collectibles, such as extra AP, MSP, and Sortie points, can be found within stages. You collect them by having units attack the spot where they're hiding. This is also how you can rescue POWs even if you don't use the Radar item.
• Rapid-Fire Fisticuffs: Ralf uses his Vulcan Punches instead of the Flame Shot if he's facing an enemy at point-blank range.
• Second Quest:
  • Beating all the stages unlocks the World 2 loop, in which enemies are stronger and have more health. To ease this, the level cap for both units and home is lifted from 10 to 20.
  • As of version 1.8.0, beating all the World 2 stages unlocks World 3. However, it also increases the base level cap to 30.
• See You in Hell: Said by Allen and his son upon dying yet again.
• Sequential Boss:
  • Crablops. When its initial health reaches zero, its bottom will be destroyed, but its top will fly off and turn into another high-health unit, similar to being the second and third boss of Metal Slug 7.
  • Emain Macha ("Twins") essentially works like this. When it's deployed, it only sends out the first, green-coloured one. When that is destroyed, the second, much faster-moving one comes charging from behind the base and fights similarly to the first otherwise.
• Shows Damage: Tetsuyuki and the Metal Claw are examples of units that get visible damage as they lose HP.
• Skill Gate Characters: Leona. She costs 80 AP, can destroy early units and bases with ease with her powerful melee attacks and special, and is very hard to handle with a beginner's deck. She falls against more experienced decks due to being melee-only- once Claw Robot and Utan are out, she becomes easy to take care of. Until the sequel, that is.
• So Last Season:
  • Happens often especially when new and very powerful units come out, being able to counter or eclipse other units' performance.
  • When Rebel Gigant came out, Patrol Robot was made pretty much useless thanks to the Gigant's special ability being able to penetrate through to hit and destroy them. Both Slug Gigant and Rebel Gigant could easily kill off air units, severely limiting the usefulness of them.
  • Before a good number of the later boss units were released, Jupiter King was an extremely good, durable and powerful unit. Now it's been Overshadowed by Awesome by a huge number of later bosses, not helped by the fact that it doesn't have a regular attack.
• Stationary Boss: Tetsuyuki, a fallen warship used as a base by the rebels in Metal Slug 1. Every once in a while it shoots an unavoidable laser.
• Stone Wall:
  • Units that have tons of HP but have little attack power on their own, such as the Giant Caterpillar and the Mars Mecha. They are essential for protecting your more powerful units from harm so that they can deal more damage before they get destroyed. The Ohumein-Congas and the Giant Caterpillar are notable for having a special attack that brings them directly to the front of your attack force, shielding the rest of your units from attacks. Donald Morden can also be used to stone wall (albeit a very expensive one), simply for having the highest HP among all units.
  • The Augensterm, introduced in version 1.7.0, is the very definition of stone wall, having the tallest hitbox in the game and the second highest HP count while being cheaper than Iron Nokana. It has the tremendously useful knockback immunity seen in previously mentioned stone wall units, and can move while laying down machine gun fire if it is not close to the enemy.
  • The Morden Robot, introduced in version 1.8.0, can be used as a cheap and spammable stone wall, having the HP of a midrange tank unit and possessing knockback immunity. When it is damaged, it launches its own head like a grenade and continues to limp towards the enemy to delay their advance.
• Take Cover!: It's good practice to hide long-range units behind big, beefy units. Snipers actually use this as their special ability: they hide under a wooden box, turning themselves into stationary turrets who can take potshots from behind the rest of the army.
• Tank Goodness: Many tanks from the series are available here, from the cute SV 001 to titanic machines such as the Iron Nokana and the Metal Rear.
• Team Spirit: If a deck consists of a single faction, they all gain a 10% HP bonus.
• Teleport Spam: The Mars People Cadre do this while firing a barrage of alien spores as their special attack.
• Temporary Online Content: Event units, who are available to purchase within a certain version.
• This Is a Drill: The Drill Slug uses its drill as a middle-range charged attack.
• Timed Mission:
  • The fight against Tetsuyuki has this sense of urgency, due to the boss being able to use a laser that hits the entire field.
  • Multiplayer battles have a 99 seconds time limit and some missions require the player to survive until the countdown ends.
  • Mission Mode consists of nothing but these kinds of missions, as detailed under Bonus Dungeon.
• Throw-Away Guns: The four main heroes typically throw away their special weapon upon use.
• Throwing Your Sword Always Works: The Arabian Soldier unit throws his sword as a special attack. His in-game description casts doubt on the usefulness of such a move. He does replace his sword after throwing it, though.
• Turns Red:
  • Subverted by the Iron Nokana. It is supposed to lift itself and reveal a flamethrower on its bottom when low on HP, but as here the flamethrower is its special move instead, its death animation shows it lifting only to immediately explode.
  • Allen O'Neil surprisingly never changes color at all despite doing so in the main series. However, his very red form has been turned into a separate unit, called Allen Wrath.
  • Allen Jr. will switch from his Gatling gun to his knife once he revives.
• Victory Pose: Done by any unit that had an animation for this in the main games.
• Walking Tank: The Slug Gunner. The Samurai Tank, amusingly, has two people holding it to move around.
• A Winner Is You: Defense reuses the ending scene form Metal Slug 3, while talking about how the heroes will continue to battle any evildoers. The same ending plays on all three loops.
• Worthy Opponent: An interesting case where your online opponent is such- you can click a "Good Job!" button telling them that they did well against you regardless of victory/loss.
• Year X: The game takes place in 20XX.
• You Require More Vespene Gas: Unit creation costs AP, which increases with time and as enemies are killed. When you have enough AP you can also spend it to make it recharge faster. One of the usable items begins levels with a maxed AP regeneration.
• Zerg Rush:
  • The descriptions for the basic Soldier and the Rebel Infantry advise this strategy, as they cost only 30 AP and have little delay between uses. A shower of their grenades sounds good in theory, but it doesn't work so well in practice because they're fragile close-range fighters. The Rebel Rifleman is a more useful unit for this strategy, as explained above.
  • Zerg rushes can also be used with any unit that has either "Fast" or "Very Fast" production speed. With the recent updates, there are now a lot of units that qualify for zerg rushes, leading to the rise of "Rush" decks.

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