From the Super Mario Wiki
Robo-Kritters are robotic Kritters in Super Mario Strikers. They are the goalies in the Super Team. While they are no different from the normal Kritters in the game, the only difference is that they're robotic. Also they never appear or can appear to play any other position. This is their only game appearance.
The Robo-Kritters could be related to Krobots, which are also robotic Kritters.