We are make a Game Jam. With a Theme, and a Mechanic. You can choose that Genre you make. For Example a Puzzle Game combined with a Platformer. 

The Mechanic is:

Upside down.

With this Mechanic you can make a great Game. As Example you press a button and the Player is going to be upside down. You can make with that a Puzzle Game. I recommend you, to do a 3D game, because you can make great Obstacles. But it is not a must. You can Choose on of these Themes:

Puzzle, or Platformer.

Or both.

Good Luck!