The Koopa Troopas are turtle-like creatures originating from the Mario games. They first appeared in the very first Super Mario Bros. game, and have appeared many more times after their debut. They are common enemies.
There are two main types of Koopa; Red Koopa and Green Koopa. There are also two main varieties of Koopa; the Koopa Troopas and the Parakoopas. The Red Koopa Troopa just walk along, but when they come to an edge they turn around and go back. Green Koopas on the other hand keep walking other the ledge, even to their death. The Parakoopa, which have wings and can fly. The red ones fly back and forth or up and down when the green ones bounce along the ground. When they are jumped on they loose their features and become a regular Koopa.
If a Koopa is jumped on then it will retract into its shell. If it is hit again then it will shoot off at a high speed, which is dangerous to the character. In Super Mario World 2: Yoshi's Island; if a Koopa is jumped on then it will be forced out of its shell. Koopas without shells wear boxing shorts. If it gets back to its shell then it will enter it again. When Yoshi swallows a Koopa, he cannot turn it into an egg and he can only have it in his mouth to spit out. However, if a Koopa has been forced out of its shell than it can be swallowed and made into an egg.
In the Mario Sports games Koopa is usually Yoshi's partner and friend. But this Koopa is probably another legion of Koopa that isn't in Bowser's command.
Koopa Troopas and Parakoopas are references to army soldiers (troopers and para troopers). Some Koopas have spikes on their backs so they can't be jumped on (though this type is never encountered by Yoshi). Other enemies are also turtles, such as Lakitu.
The King of the Koopas is Bowser. Other notable Koopas are the seven Koopalings, Bowser Jr., Hookbill the Koopa and Knot-Wing the Koopa. Koopa Troopas also appear in Super Princess Peach in two forms and states. Normal ones walk normally while happy-singing ones jump after a walk.
Koopa Troopas are rare enemies first appearing in the level Visit Koopa And Para-Koopa they come in two colors red and green they can be knocked out of their shells turning them into a Beach Koopa.
Koopa Troopas reappear in Yoshi's Island DS they are given an increase in size but otherwise behave like their predecessor.
Koopa Troopa reappears in Yoshi's Woolly World they only come in a red variant but otherwise behave like they do in previous games they first appear in the level Knot-Wing the Koopa's Fort.
Koopa Troopas reappears in Yoshi's Crafted World they only appear in one level Many Fish in the Sea acting the same as before they once again come in red and green variants.