History VideoGame / MetalSlugDefense

* MilestoneCelebration: To celebrate the 20th anniversary of ''VideoGame/TheKingOfFighters'', 6 fighters (Kyo, Benimaru, Goro, Iori, Vice, and Mature) were added to the game as purchasable units.

* [[EvolvingCredits Evolving Title Screen]]: Clearing World 1 makes a grieving woman appear on the title screen. Clearing World 2 makes a UFO fly by in the background.

* AlwaysAccurateAttack: 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.

** 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.

** Patrol Robots. They don't have much health, 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.

** Patrol Robots. They don't have much health, but their attack has very long range, deals very good damage, and also pushes back enemies very well. They're pretty slow too, however, so you'll need to defend them with more durable units.

* FinalBoss: [[spoiler:The final set of boss enemies at Final-5 in World 3 are Iron Nokana+Allen and then Morden+Jupiter King, supported by hordes of zombie alien clones of Fio.]]

* 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.

** Gunnner Units have a powerful punch as their standard attack.

* ActionBomb: The Zombie Rebel Soldier, Mutated Soldier and the Hopper Mecha units self-destruct upon reaching a target. The player can also release an explosive SV 001 once its meter is filled.

* {{Cap}}: The level cap for units and the player base's attributes is 10, but it expands to 20 once the second loop is unlocked, and can be upgraded to 30 by paying with Silver Medals. 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.

* FinalBoss: [[spoiler:The final set of boss enemies at Final-5 in World 2 are Iron Nokana+Allen and then Morden+Jupiter King.]]

** The Commander is rather fragile for a 250 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.

* LightningBruiser: The Natives, introduced in version 1.4.0, have 200 more HP than Chowmein-Conga (which has the highest HP for a 40 AP cost) and a faster speed in exchange for only 5 more AP cost. Their standard attack is above average for an infantry unit while their special attack has a ridiculous range and deals even more damage.

** With the 1.5.0 update, random collectibles ranging from MSP and extra Sortie points can be found within stages. You collect them by having units attack the spot where they're hiding.

** As of version 1.18, eating all the World 2 stages unlocks [[HarderThanHard World 3.]]

* [[spoiler: AWinnerIsYou: The game 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 both loops.]]

** Zerg rushes can also be used with any unit that has either "Fast" or "Very Fast" production speed. With Mutated Soldiers now buffed to have "Very Fast" production, it's possible to ZergRush with suicide units.

* FinalBoss: [[spoiler:The final set of boss enemies at 16-5 (second loop) are Iron Nokana+Allen and then Morden+Jupiter King.]]

* EvolvingTitle: Clearing World 1 makes a grieving woman appear on the title screen. Clearing World 2 makes a UFO fly by in the background.

* ChargedAttack: Most units can use a special move by spending a meter that fills over time. Oddly, few CPU

* AscendedExtra: Sandbags, usually used by granede-wielders of the Rebel Army for protection, are an essential tool for survival in this game.

* BribingYourWayToVictory: Silver medals can be used to buy items that grant advantages in the missions, such as [[TooAwesomeToUse 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.

* {{Cap}}: The level cap for units and the player base's attributes is 10, but it expands to 20 once the second loop is unlocked. 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.
* ChargedAttack: Most units can use a special move by spending a meter that fills over time. Oddly, few CPU characters use their special move.
* TheComputerIsACheatingBastard: For some reason, the CPU doesn't use special moves even in the second loop but it does work [[MyRulesAreNotYourRules 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.
* DefeatMeansPlayable: Clearing a set of levels usually means unlocking the enemies featured in them... [[DoubleUnlock 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 and Huge Hermit are unplayable due to being overpowered living bases. For some reason the trains from the subway levels can't be unlocked (yet?) either.
* DualBoss: Some missions like to spawn large enemies such as Shoe and Karn or all three Ohumein-Conga at once at some point.
* EliteMook: 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.
* EverythingsBetterWithMonkeys: Utan, lover of bananas, is unlockable from the beginning.
* EverythingsDeaderWithZombies: The zombie enemies from ''Metal Slug 3'' are present. This includes Zombie Marco, who can vomit a danguerous jet of blood.
* EverythingFades: Dead units may [[NoBodyLeftBehind fade, melt or explode.]]
* EvilLaugh: Allen ''frequently'' laughs while attacking. Morden only laughs in his victory pose.
* ExcusePlot: Morden and the martians are up to no good, so send waves of units at their bases.
* ExtendedGameplay: 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.
* ExtyYearsFromNow: The game takes place in 20XX.
* FailedASpotCheck: 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.
* FlavorText: Each unit has a description about who they are and what they do.
* FinalBoss: [[spoiler:The final set of boss enemies at 16-5 (second loop) are Iron Nokana+Allen and then Morden+Jupiter King.]]
* GatlingGood: Units such as Marco, some Slugs and Allen wield this weapon either normally or as their special attack.
* GlassCannon: 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 250 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.
* TheGoomba: 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 granades. The green normal rebel soldier is an unlockable and he has even less health (360 at level 20) for an even lower price.
* HarderThanHard: There are three difficulty levels beyond Hard: Very Hard, Expert, and Hell.
* HitboxDissonance: 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.
* HumongousMecha: [[http://metalslug.wikia.com/wiki/Jupiter_King 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.
* IdleAnimation: 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.
* ImmuneToFlinching: 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.
* InfinityPlusOneSword: 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.
* InsurmountableWaistHeightFence: Sandbags block enemy advances until they're destroyed. In normal ''Metal Slug'' games, people would just jump over them instead.
* KamehameHadouken: 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.
* KnowWhenToFoldEm: [[http://metalslug.wikia.com/wiki/Abul_Abbas Abul Abbas]] waves a white flag and disappears when out of HP.
* LightningBruiser: The Natives, introduced in version 1.4.0, have 200 more HP than Chowmein-Conga (which has the highest HP for a 40 AP cost) and a faster speed in exchange for only 5 more AP cost. Their standard attack is above average for an infantry unit while their special attack has a ridiculous range and deals even more damage.
* LimitBreak: A [[ActionBomb 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 [[InstantDeathRadius 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.
* LuckilyMyShieldWillProtectMe: 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.
* MadeOfIron: For obvious reasons, Allen O'Neil, a barechested soldier, has HP comparable to that of a heavy tank.
* ManOnFire: 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.
* MegatonPunch: Ralf has the notorious Galactica Phantom punch as his special attack.
** Gunnner Units have a powerful punch as their standard attack.
* MightyGlacier: 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 comes with tons of HP, resists knockback, 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.
* MookMaker: 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.
* {{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.
* NonLethalBottomlessPits: 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.
* NostalgiaLevel: 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.
* OhCrap: If a sandbag man gets hit before setting a barrier, he freaks out and flees. Rumi is also shown panicking in her icon if a mission is lost.
* OneHitPolykill: 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.
* RandomlyDrops: 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, [[FakeLongevity to force replays.]] It's [[LastLousyPoint especially annoying]] in regards to [[ThatOneLevel the harder]], [[AntiPoopSocking expensive]] missions and the bonus ones that are only available for a short time on each day. Of course, you can use [[BribingYourWayToVictory 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 ranging from MSP and extra Sortie points can be found within stages. You collect them by having units attack the spot where they're hiding.
* RapidFireFisticuffs: Ralf uses his Vulcan Punches instead of the Flame Shot if he's facing an enemy at point-blank range.
* SecondQuest:
** 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 1.18, eating all the World 2 stages unlocks [[HarderThanHard World 3.]]
* SeeYouInHell: Said by Allen upon dying yet again.
* ShowsDamage: Tetsuyuki and the Metal Claw are examples of units that get visible damage as they lose HP.
* StationaryBoss: 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.
* StoneWall: 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.
* TakeCover: 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.
* TankGoodness: 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.
* ThisIsADrill: The Drill Slug uses its drill as a middle-range charged attack.
* TimedMission:
** The fight against Tetsuyuki has this sense of urgengy, 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 BonusDungeon.
* ThrowingYourSwordAlwaysWorks: The Arabian Soldier unit throws his sword as a special attack. His [[FlavorText in-game description]] [[LampshadeHanging casts doubt on the usefulness of such a move.]] He does replace his sword after throwing it, though.
* TurnsRed: 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.
* VictoryPose: Done by any unit that had an animation for this in the main games.
* WalkingTank: The Slug Gunner. The Samurai Tank, amusingly, has two people holding it to move around.
* [[spoiler: AWinnerIsYou: The game 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 both loops.]]
* YouRequireMoreVespeneGas: 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 [[BribingYourWayToVictory begins levels with a maxed AP regeneration.]]
* ZergRush: 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 granades 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 Mutated Soldiers now buffed to have "Very Fast" production, it's possible to ZergRush with suicide units.
----

** 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 eight total: 4 for both Worlds 1 and 2.
** World 3 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 HarderThanHard.

* SecondQuest: 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.

* TimedMission: The fight against Tetsuyuki has this sense of urgengy, due to the boss being able to use a laser that hits the entire field. Also, multiplayer battles have a 99 seconds time limit and some missions require the player to survive until the countdown ends.

* TheCameo: Every heroic character from the series is at least mentioned in the game, even those from the ''Mission'' and ''Advance'' spinoffs or the Ikari Warriors (including Whip and Heidern). The villain side doesn't get such attention, though recent updates have been trying to rectify that with new units and extra missions.

* BonusDungeon: 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 four in total.

* LightningBruiser: The Natives, at least when they were introduced, has 200 more HP than Chowmein-Conga (which has the highest HP for a 40 AP cost) and a faster speed in exchange for only 5 more AP cost. Their standard attack is above average for an infantry unit while their special attack has a ridiculous range and deals even more damage.

* ExtyYearsFromNow: The game takes place on 20XX.

* LightningBruiser: The Natives, at least when they were introduced, had 300 more HP than Chowmein-Conga (which has the highest HP for a 40 AP cost) and a faster speed in exchange for only 5 more AP cost. Their standard attack is above average for an infantry unit while their special attack has a ridiculous range and deals even more damage.

* StoneWall: 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 stone wall (albeit a very expensive one), simply for having the highest HP among all units.