You can add 5 more characters to the roster. Anyone you want but they have to have their first appearance be in a video game. Include the stage they would come with too. Here are my 5.

Dante from Devil May Cry. Stage: the top of the tower from DMC3. (I know the name of the tower, I jist forget how to spell it)

Jinx from League of Legends. Stage: Summoner's Rift or The Last Drop in Zaun

Shadow from Sonic the Hedgehog. Stage: Radical Highway