I don't necessarily support/think these characters have that much of a chance, btw
Paper Mario - flips in as in Super Paper Mario when using Fleep
Simon Belmont - ummmmm... I can't think of anything more interesting than him just jumping in, appearing in moonlight, warping in ala Ike's appearance, etc.
Pac Man - the reverse of the death animation from the original games
Moogle or Black Mage - rides in on a chocobo
Chocobo - just rides or flies in
Crono - a time portal appears (preferably with an appearance pretty similar to the way they look in the SNES game with the accompanying sound) and Crono steps out of it
any Kong - appears out of a DK barrel
Pokemon Trainer - appears out of a pokeball! And then throws a pokeball releasing whichever one of Squirtle/Ivysaur/Charizard! Cuz that would just be hilarious. In reality, he'll probably just already be in the background when it zooms in on him, and he'll just throw the pokeball and such.
Zero Suit Samus - probably the same as Samus (assuming there's a way to start as her). So appearing out of a save station. Possibly appearing out of a save station and her suit dropping off. Or possibly jumping out of her ship.
Sheik - with a smokebomb, all ninja-like
Link and WW Link - appearing out of a column of light, coming from a warp tornado or something like that. They might go TP for Link and have him appear out of one of those black sky things. And WW Link's warp tornado could have that cyclone spirit guy in it.
Game & Watch - uhhhhhh... I dunno. A G&W portable game being held by human hands is pressed against the screen, and then removed, but G&W remains on the screen after the game is removed.