^Hey, Skunktank only has one weekness. It's kinda tough if you don't have a ground type. Also, normal types get the HUGEST list of other attacks they can learn. Look at almost any normal type's attack list, and you'll most likely get a surprise or two.
Anyway, weakest type... I would have to say... fighting. Why? Because, fighting types, although they have quite a few super-effective hits, most of them have almost non-existent defence stats. Except, say, Lucario, but he's trumped by other fighting types. Oh, and besides, Lucario has steel to back him up. Also, it just so happens, psychic and flying, fighting's weaknesses, happen to be some of the fastest pokemon out there. Meaning they normaly get whiped before being able to lash out one last time... I pity them. >>