All-Stars X Smash Bros: Master Polygon

The final boss for my idea of a PlayStation All-Stars and Super Smash Bros crossover, Master Polygon is the alliance of Master Hand, Crazy Hand, and Polygon Man, (the recently announced final boss of PlayStation All-Stars). Since Tabuu was defeated in Brawl, he isn't part of this alliance, but does return as a neutral party.

The story of how such a crossover could commence (ignoring copyright issues), is that the inclusion of third party characters and the defeat of Tabuu in Brawl opened up the video game multiverse. Polygon Man's creation of the All-Stars universe would coincide with Tabuu's defeat, thus (in a manner similar to MK vs DC) opening the worlds of Nintendo and Sony to each other with the link created by the inclusion of Metal Gear characters in both.