Do the following achievements to get the result needed:
Kevin Nash: at any game menu press L, X, Z, Y.
Ric Flair: complete Season Mode with The Big Show, Rob Van Dam and Triple H.
Lita: complete Season Mode with Matt Hardy.
Christian: complete Season Mode with Chris Jericho.
Vince McMahon: complete Season Mode, facing Vince in the final battle.
Stephanie McMahon: complete Season Mode with Kurt Angle.
Hulk Hogan: complete Season Mode with The Rock.
Pick Level: use any character to Finish Season Mode.