-Tabuu, Master Hand, Crazy Hand, Galeem, and Darkon resurrect.
-Mission is to make an alliance and take over the entire video game multiverse.
-Wibbly wobbly timey wimey stuff causes the different video game universes to merge in the first place.
-They initially win, taking over society like it's 1984.
-Original 8 (Mario, DK, Link, Samus, Yoshi, Kirby, Fox, Pikachu) form a resistence to lead the charge against the big 5 baddies and free everyone from the dystopian world.
-Each of the original 8 can also have a branching path and different plots, similar to Subspace Emissary. Inserting a little character development too will help, since Lucas and King Dedede were two of the only characters with any kind of development in SE, maybe THE only 2.