Culex is a pain to me unless I'm uber-cheap and put the Lazy Shell Armor AND the Safety Ring on Toadstool, the healer/reviver of the group, and then have a magically/physically proficient Geno and a physically proficient/semi-magical(for jumping) Mario in the same group; a magical Mallow in place of Geno also works well. I haven't tried beating it without Toadstool yet(Peach? Yes, but she was Toadstool to U.S. players back then), but besides what I metioned there's also cheap item tactics you can use to defeat him as well. Other than that, yeah, he raped me pretty good the first time I went up against him. XD
Jinx? Blocked all his attacks, no Safety Ring required. Next!
