Probably the greatest mod ever created; improves Brawl in every conceivable way by adding 100+ new stages, changing the system mechanics/balance, creating new moves and character animations & Knuckles. P+ isn't just a port of melee's mechanics onto Brawl's engine, it's clearly it's own game with thousands of hours of collective work and more passion behind it than a certain billion-dollar corporation will ever have (you can even play Brawl's single-player modes and more if you're into that).