They're practically indestructible. They need to be killed many times, if that makes any sense. Like Lust--Roy actually finished her off, but I heard it took a lot of "killing" her.

[He shakes his head, glaring down a bit.]

I've fought a few of them... they're not easy to take on alone, I've never managed. We were actually fighting that fat one, Gluttony, right before I came here, Ling, Al, and I.