Wong fights similar to both Sion and Dauragon. He uses the same two-fisted attack as Dauragon (where he can hit an opponent both in front of him, and behind him), as well as leg sweeps similar to Sion. You can use normal attacks against him, but one special move in particular works very well.
Block attacks from Wong, and while he is recovering from one press the ES+MEDUIM buttons (whatever you have them assigned to) to perform the Torpedo Kick move, which will take off a bit of damage and knock Wong off his feet. Turn that into a pattern: Block, Torpedo Kick, Block, Torpedo Kick, etc. to defeat Wong, who you can then use in the Versus mode.
Successfully complete the game (not in story mode) once to unlock Echidna, Dauragon1, Dauragon2, Dauragon3, Mogetsu, Mogetsu unmasked, PD-4, Dominique, and Kaldea.