Since the GC["N"] has up to 15 times the memory of the N64, Mario Kart Cubed should have more characters than any previous MK game. This would also add some to the replay value. My all-star list of characters:
Donkey Kong
Mario
Luigi
Yoshi
Bowser
Peach
Toad
Wario
Waluigi
Koopa Troopa
Goomba
Link
Zelda
Diddy Kong
Kirby
Samus Aran
Fox McCloud
Pikachu
Jigglypuff
Mewtwo
Snorlax
Ness
Daisy
Bob-Omb
And the sole unlockable character:
Blue Yoshi! (Didn't see THAT coming, did you? Ooh, stealthy!)
Some track ideas:
Star Way (Paper Mario)
Fairies' Woods (Zelda: Oracle of Ages)
some of the sliding levels from SM64
Also, I think there should be more combat this time around. Bowser could use his fire breath to toast the competition around him, Yoshi could trap other racers in eggs for a few secs., Zelda could transform into Sheik and drive a lot faster, etc. And there should be a bit more difference between between characters. There's something mighty suspicious about captain of the burger-munching, fat-Elvis brigade Bowser jumping as high as light-as-a-feather Toad. Some new item ideas:
Fire Flower (burn all nearby enemies)
Super Mushroom (grow 3x your size)
Cape Feather (jump 3x as high and stay in the air longer)
Bomb (send the next enemy who dirves past it flying into the air)
Star (not Starman) (get teleported in front of the leader)
Yoshi Egg (Hit a nearby enemy or obstacle or wall with an unborn Yoshi in an egg, upon which the egg will burst open, and Yoshi will swallow the next racer that drives by)
Hope you liked my ideas. I know I do. Yordle yordle yordle. Wahoo!
Sniff sniff... do I smell a Lucky Fruit? Wahoo!
