If you dodge roll twice out of the way of it's beam, you can do a punisher to break it's legs and cripple it slowing it down for the rest of the fight. With the cripple debuff you get to deal more damage too.
The vampire staff is really good early game so a lot of people see it as a crutch and keep it, but the percentage of life you get per hit is so low that eventually is basically imperceptible. Generally you want any weapon with bleeding or cripple for later game.
