New member here. Anyway, these are some of the characters I'd like as DLC:
Captain Syrup (Wario Land)
Ayumi Tachibana (Famicom Detective Club part 2)
A Resident Evil character (preferably a female one like Jill or Ada)
Another F-Zero rep (Pico, Black Shadow, Goroh, just to name a few)
Another Punch Out rep (Super Macho Man, King Hippo, Great Tiger, Vodka Drunkenski, Doc, etc)
The Lost Vikings (from, well, The Lost Vikings)
Bad Mister Frosty (Clay Fighter)
Waluigi
Alexandra Roivas (Eternal Darkness)
Raimi (Geist)
Another Metroid rep (Dark Samus, Sylux, etc)
Another Street Fighter rep (Chun Li, Cammy, Zangief, etc)
Phoenix Wright (Ace Attorney)
Red Arremer (Demon's crest)
Arthur (Ghosts'N Goblin)
Earthworm Jim (Earthworm Jim)
Boogerman (Boogerman)
Crypto (Destroy All Humans)
Simon Belmont (CastleVania)
Another CastleVania rep (Sypha, Shanoa, Alucard, etc)
These are just the ones at the top of my head right now.