Oh, yeah, almost forgot:
Crash Bandicoot - Playstation All Stars Battle Royale 2
All the TMNT and the other 2 Battletoads characters in Killer Instinct so that we could finally have the dream match-up: TMNT vs Battletoads.
Any Eternal Champions characters (mostly Trident) in Mortal Kombat, since both series are extremely violent and gory.
Frank West for Street Fighter x Tekken and a Xbox exclusive character for both this game and Mortal Kombat 9
Any Sega characters for Dengeki Bunko Fighting Climax: Ignition
Any BlazBlue character for Tekken 7