Np mate
Yeah thats true, Vamp is very fast, and very hard (maybe even impossible) to kill, but:
Psycho Mantis can tell what people are going to do with his psychic powers, and Vamp can tell what people are going to do by predicting where their muscles will go etc
So both will just stand there trying to predict each others movements
and then it would go all crazy
E.g Vamp throws his knife, and psycho mantis predicts and dodges it, but Vamp predicts where he's going and throws his knife there, but Psycho Mantis predicts that and... well so on.
Thats just my theory, though