Each mouse axis (horizontal/vertical) would count as one button (or even two), so mouse movement + left and right click would be 4 or 6 buttons!
Usually the games in this jam don't use the mouse movements.

BUT you can have several keys acting the same way, so that people can play with their favorite part of the keyboard.

Examples:

- A and D (for Qwerty)
- Q and D (for Azerty)
- K and L
- left arrow and right arrow
- left click and right click

You can implement all of that at the same time in your game, it will still count as two buttons!