Obviously hasn't faced a well-played Extremekiller/Dark Arceus.
True, I've never seen it played well, so I may be biased. Competitively, I've never used Arceus or seen someone who's used it, so when I battle n00bs who use him simply because he's got, I just gut him. I can't seem to make him work for me, though.
Oh, and Shaymin-S belongs up there with those utterly broken legends. Forgot to mention it.