Items appearing in Max will include all the items from Brawl. Also, the Red Koopa Shell and the Melee bumper. This means that both bumpers appear in Max. there will also be new items, assist trophies and pokemon.
The new items are:
Hydra/Hydra Parts(Kirby Air Ride)
Ice Flower(Super Mario Galaxy)
Volt Shroom(Super Paper Mario)
Rolling Pin(Cooking Mama)
Plunger(Rayman: Raving Rabbids)
Giant Nintendo DS Stylus(Nintendo DS)
Guitar Hero Controller(Guitar Hero)
Tennis Racket(Wii Sports)
Dagger of Time(Prince of Persia:Sands of Time)
All the assist trophies (except for Shadow, Samurai Goroh, Saki Amamiya and Little Mac) return in max.For list of new assist trophies and what they do, click this link.
All the pokemon (except for Deoxys and Meowth) return from Brawl. In addition, Articuno, Zapdos, Raikou and Chansey also return. For a list of new pokemon and what hey do, click this link.