so wold slaughter vampire just flat out kill them, or does it do dame = force or what???

Besides that I forgot how damage works for spells, I once assumed that damage = drain
damage in = damage out.

It's just like the spell description says; Manaball with a Restricted Target limitation that lowers the drain. It is otherwise identical to Manaball in every conceivable way.

Dr. Funkenstein is correct.

The 'name' is meaningless. you could call it Van Helsings gze if you wanted to.....

The effected is a target restricted manaball.

It functions exactly like a manaball damage Force+Net hits (as long as net hits >0), save that only vampires would be effected.