In Super Smash Bros.
Two Green Koopa Troopas as 8-bit sprites walk back and forth in the background of the Mushroom Kingdom stage. They do not affect gameplay in any sort of way.
In Super Smash Bros. Melee
The Koopa Troopa makes an appearance in the first stage of Adventure Mode, where they walk back and forth. If you make contact with them, you will take damage. Simply just attack them to make them retreat into their shells. You can pick up their shells and use them like the Green Shell item. Although if the shell is red from a Red Koopa Troopa, it will function like a regular Green Shell, but also burn people. The only difference is that the shells from the Koopa enemy don't disappear. The reason is after a short amount of time Koopa will come back out of its shell and walk back and forth again. This can happen even when the player is holding the shell. To permanently get rid of them you must throw them by picking them up with the "Z" button. You can throw them at your opponents to give them a good amount of damage and maybe even defeating them at low percentages.
Their stance they take in Melee is a crouching but walking on two legs, which is a mix between the original which they walked on all fours, and Super Mario World, which they had walked upright. Also, one 8-bit Green Koopa Troopa cameos in the background of the Mushroom Kingdom stage.
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.
In Super Smash Bros. Brawl
Koopa Troopas make an appearance in Super Smash Bros. Brawl's Adventure Mode: The Subspace Emissary. The green archetype appears as a ground enemy in stages where Bowser's minions are present. Unlike their Melee counterparts, Koopa Troopas will not harm players that walk into them. Instead, they attack with a leaping headbutt. Once they are stepped on, the shell can be used as an item.
Koopa Troopa (Green) Trophy Description
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.
- Super Mario Bros., 1985
Koopa Troopa (Red) Trophy Description
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.
- Super Mario Bros., 1985
In Super Smash Bros. for Wii U / 3DS
Koopa Troopa (Green)
Koopa Troopas are the main representatives of Bowser's army. They are just about as common as Goombas. They know no fear, bravely charging ahead even if it means falling off a cliff or into a hole. They do this in Smash Run as well. Defeating them will reduce them to a shell you can throw.
Koopa Troopa (Red)
Bowser's go-to foot soldiers. They sport red shells and advance forward, but they have the common sense not to walk off cliffs. During Smash Run, they'll advance toward any fighter they see, attacking with their whole body. These Koopas leave red shells when beaten.