I really love the idea!
The lost golden tooth
This game is a two players platformer.
The first player is on desktop, and move a wizard into a world infest by goblins. He is helped by the second player on mobile, who playing a fairy. The mobile player is able to launch spell to kill goblins or help wizard to progress and kill the boss.
You can see the game on http://vps326956.ovh.net:8080/