When he's already there he leaves when the monster dies but due to terrible luck or something I've killed the monster just as he arrives twice and it takes a minute or two for him to stop attacking when he makes his first appearance. I was in MP the second time it happened and the other guy got one carve and I got zero again :/
He was pretty interesting as an invasion monster at first but now that I'm at the point where he doesn't pose a danger he's just an asshole who's constantly crashing the party to steal my thunder. Super annoying.