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.
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.