Sucking Mateo's blood would be more effective if it weren't for his habit of going hungry before a hunt- when he's low on blood, his senses are better and he has slightly better reflexes. There is little blood to be had, unfortunately. The toxin, though? That's quite effective. More effective than any other type of poison; his undead physiology can ignore those without difficulty.
Mateo tries to lurch himself forward, using the creature gripping his leg as a pivot to escape from the one trying to hamstring him. If the move is successful, Mateo will wind up lying on his front and apparently hampered that way.That won't work as the hamstringer is the one wrapped around his leg. The toxic sliver is successful, though Mateo's unconcerned, for now anyway. The dazed vampiric sliver is Mateo's more immediate worry- whilst it's harmless for now, it won't be soon. So Mateo will do something about that- he moves his arm closer and bites at it, trying to return the favour and slurp its blood until it's dry. Unless the blood starts rotting his face off, anyway. This might have the added benefit of helping Mateo recover from his wounds as the blood is converted to fresh, healthy tissue- notably, around the bite taken from his arm and his crippled leg, though Mateo tries concentrating it on his leg. It'd be more successful if the slivers were humanoid, but Mateo's used to using the blood of animals after particularly challenging fights.