Worlds collide

Strange things start to happen in the afternoon. Portals opening, memory's being messed up, new evil villains. How can they save the day and get back to their world?
This is my very first story. Please enjoy. This story contains the characters Sonic, Tails, Dark Sonic, Ford, Dipper, Mabble, Bill, Bipper, Harry, Draco, Ron, Hermione, Sans, Frisk, Chara, and Bill Sans.