Koopa Troopas first appeared in Super Mario Bros., and, along with Goombas, are some of the most common and recognizable enemies of the Mario series. Mario is able to stomp Koopa Troopas into their shells and kick these shells as projectiles. However, the shells can also pose a danger to Mario if they bounce off of a wall. In later games, Mario is also able to pick up and carry around their shells: this, however, can be dangerous, as the Koopa in the shell wakes up after a short while. Green Koopa Troopas in Mario games don't turn around when reaching a cliff and just fall down, unlike their Super Smash Bros. version.
Their design in Melee is a hybrid of their Super Mario Bros. version, where they walk on four legs, and their later bipedal look introduced in Super Mario World. Their design in Brawl and SSB4 is exclusively taken from the newer games.
Two Green Koopa Troopas resembling their Super Mario Bros. 8-bit sprites walk back and forth in the background of the Mushroom Kingdom stage.
Green-shelled Koopa Troopas and Paratroopas (and a single Red-shelled Paratroopa) populate the first stage of Adventure Mode. They walk back and forth, turn around at ledges and hurt the player on contact.
Dealing enough damage to them or jumping on them makes them retreat into their shells. The player can pick up their shells and use them like the Green Shell item to KO other enemies or damage opponents. The Red Koopa Troopa's shell acts similarly to the other green shells on the stage, but it also deals flame damage.
Koopa Troopas will eventually come back out of their shells and walk around, even if the player is holding the shell. To actually defeat a Koopa Troopa, the player must grab and throw it, or knock it off a ledge.
Common soldiers in Bowser's army, Koopa Troopas can retreat into their shells. Unbelievable as it may seem, they're clearly unaware of being kicked and sent sliding when in this position. There are many Koopa types, each with a different shell color and unique traits. They all wear T-shirts and shorts under their shells.
Koopa Troopas make an appearance in Brawl's Adventure Mode: The Subspace Emissary. The green and red versions appear as ground enemies in stages where Bowser's minions are present. Unlike their Melee counterparts, Koopa Troopas do not harm players on contact, but they attack with a leaping headbutt when close enough. Like Goombas they are vulnerable to jumping, and get into their shells when stomped. The shell behaves exactly like a normal Green Shell.
A henchman of Bowser. In the old days, they'd retreat into their shells for a short while to protect themselves after being stepped on. Recently, however, some have begun to immediately pop back out. You'll often find them marching straight ahead--if the path ends, they'll just march into the abyss. Surely there are no braver turtles to be found.
A turtle in the employ of Bowser. Koopas formerly traveled on four legs, but they've recently been spotted strolling on two. This has freed up their hands, allowing them to chase Mario with nets. Their adaptability must make Bowser very happy indeed. Unlike their green-shelled brethren, red ones do about-faces when they run out of road. They're a bright group.
Red and green Koopa Troopas appear as enemies, keeping their Brawl behavior.
The Red Koopa Troopa trophy is exclusive to Super Smash Bros. for Nintendo 3DS.