Mechakoopas resemble ordinary Koopa Troopae, but have been rendered armless in the games. Their shells are green, and a wind-up key pops out the back to allow them to keep moving.
They are wind up versions of the Koopa Troopae, but they are armless, they are mettalic, they have no spots on their shells, have metal yellow hair, cylinder prism like feet and red and black eyes that are misplaced, like the left eye facing up and the right facing down, making them somewhat cross-eyed.
Mechakoopas appeared as enemies in Super Mario World. They are only found in the Valley of Bowser's castle. They walk back and forth until Mario stomps on them, like Koopa Troopas. However, when thrown or kicked, the down slide around. They are also found in the final boss fight against Bowser. They are used as the main weapon to defeat Bowser.
Mechakoopas reappear in Super Mario Galaxy, now renamed "Mechabowsers." They gain a ability, which is to spit fire from left to right When a spin attack is used on them, their heads flip upwards. When a ground pound is used, they are instantly defeated. They are mostly found around Toy Time Galaxy.
They reappear in New Super Mario Bros. Wii, but are only found on the airship stages.
Mechakoopas reappear in Super Mario Maker 2, as part of update 3.0. There are now two variants: One that is red that can launch red missiles that home in one Mario like the Missile Bill, but explode after a short time and a blue version that can shoot lasers out of it's mouth. When in the nighttime setting, they have boosters that allow them to hover for a short time.
Mario & Luigi series
Mechakoopas also appear as enemies in Mario & Luigi: Dream Team. They are only fought in Dreamy Neo Bowser Castle in groups. In battle, they mainly attack by charging and jumping into Mario (and Dreamy Luigi). This must be blocked by jumping (hammers if they come from all four sides). They can also breathe fire which can be jumped.
Mechakoopas return in Mario & Luigi: Paper Jam, haunting Neo Bowser Castle. They attack by charging, but can be blocked by jumping or hammers. Once again, Mechakoopas will reverse their tells if the heroes make them angry.
Mario & Luigi: Superstar Saga for 3DS
Mechakoopas do not appear as fightable foes in the Game Boy version of Mario & Luigi: Superstar Saga (They were made into electricity conductors for Bowser Castle.), but can be fought in the game's 3DS version, where they haunt the Beanbean Kingdom's university, the Woohoo Hooniversity. They attack by charging, which can be jumped. Like in their previous appearances, Mechakoopas can get angry if their body is damaged too much, causing them to spark and break their charge and attack the Bro. who was not aligned with their charge at first. Strangely, Mecha-Chomps do not appear.
Mario Kart series
Super Smash Bros. series
Mechakoopas can be summoned when Bowser Jr. uses his Down Special Move, Mechakoopa. Here, they charge and explode when they collide with someone. However, they can be reflected back to Bowser Jr. Bowser Jr. can also customize his Down Special such that the Mechakoopas jump out of the Koopa Clown Car in a long jump and explode when they hit something (or someone) in a variation called Impatient Mechakoopa, or they are bigger (Big Mechakoopa). Mechakoopas can also be carried and tossed like Bob-ombs.