Forest

The sliver's arm does pass through Mateo's heart, but since I don't think the Vampire Sliver's arm is made of wood it doesn't do much. If it is, in fact, made of wood, then Mateo is paralysed and can't do much until it is removed. This includes drinking the vampire sliver's blood.

The main problem with vampires is that they have a large list of weaknesses, but if those weaknesses aren't used it's hard to stop them. Decapitation, fire and holy energy are pretty good ones, though slicing him into lots of small pieces would have been effective too.