Gotta have some Scooby-Doo action in there. His counter-move for the 15 hit super combo would obviously be stopping the oncoming character by looking at his fingernails, filing, polishing and ending with a 6-hit combo smooch on the mouth.
Must have Space Ghost, but he'll be all about the cheap long-range attacks with those wrist weapons.
Its old anime, but lets put Speed Racer in there. I've wanted to kick his pansy-ass since 1973. Heck, he can bring Pops, Trixie (sister, girlfriend, or both?), Spridle and Chim-Chim along with him. When they reach full power, they turn into Racer-X, the only character worth a darn on the program.
Finally, was there ever a "badder" cartoon character than Mr. Race Bannon, the almighty protector of Dr. Benton Quest and his son, Johnny? Race has got to be an unlockable "Boss" character. Throw in Johnny's buddy Haji, he'll be all about the judo.