Ok! I was going through FanFiction.net and founded a story which I think would be PERFECT for our favourite two heroes come together! (...other than the game series).
After a big battle against Eggman, Sonic and his friends get sucked into Mario's universe. At first, their main priority is to get back home, but they realize they must work together to stop an evil force, bigger than Eggman and Bowser's powers combined!
Tell me if you guys like it?
(Here is the link: Mario and Sonic: Heroes Unite!)