Rotion now supports 2 to 4 player splitscreen via controllers and a mouse. You can choose to have any slots played by the CPU, and there are two game modes: free for all and 2v2.
I have implemented aim assist for both mouse and gamepad controls; this has had the benefit of improving the difficulty for gamepad users from 'impossible' to 'just about competitive' against mouse users. If a gamepad is detected on the first run, the game will ask if it should be used (which can of course be changed later).
Expect a new video soon! Until then, here are some bonus .gifs;