Just take a look at the controls in the menu and read the hints displayed in the training mode. Pick a character by dragging the p1 (or p2) dot around. -Bowser JR, additional character unlock: Reach 20 points in training mode.
Welp. This is it. The final version. Put a lot of effort into this thing. So.. I hope it's somewhat enjoyable. Playing the training mode when you start playing is recommended. It'll help you understand the hitboxes and the mechanics. Please report any glitches/issues so I know whether there's still something to fix or not.