I just got my voodoo staff 2 days ago, got addicted to it, now I'm lvl 15 staff working on getting the harrow staff, although I only had to sink 2 skeleton ships to get the shrunken head, the phantoms around padres del feugo is where I got it. Anyway, the first two attacks are pretty weak, but dont give up on the staff, unlock the first two skills you get then save up the points till you get to level 4 which is when you get the attack "wither" a pirates best friends when it comes to fighting multiple enemys, dealing 300+ on its first skill point and I have 5 skill points on it and I've hit over 700 with it. then you get "flaming skull", really awesome attack also not as good as wither when fighting multiple enemys and charges a little slowly but with 4 skill points on it I'm dealing over 1000 damage with it, after that you get "banish" only works on undead and sometimes hits over 1000 on its first skill point! it's very very slow at charging though and using a heck of a lot of voodoo.
here's a quick sreenie I made after using flaming skull on a dread scorpion (I have 4 skill points on it)
(the damage dealt is 1315)
last attack in the voodoo staff is called "desolation", my friend has it, it looks awesome when you cast it, it like a big hurricane with skulls and stuff everywhere and can easily kill somthing lvl 20 or more in one hit, bad part is that is hurts the person casting it so you should have a good healer when you're casting it.
(edit)here are pictures of all the voodoo attacks I have so far from first to last:
Soul flay:
Pestilence:
wither
flaming skull:
banish:
and the last one desolation I do not yet have