Uncle Grandpa is driving his RV when he accidentally gears it to smash through the other Cartoon Network universes, unknowingly picking up Gumball, Clarence, Steven Universe, Mac & Bloo From Fosters Home For Imaginary Friends, Dexter, Mordecai and Rigby from Regular Show, and Finn and Jake from Adventure Time. They then have to set out to defeat an army of "Mirror Clones", evil shard clones presumably formed after breaking through the dimensions.
