Necromancer's Siphon

{t}: Put a charge counter on Necromancer's Siphon if you cast a black spell this turn.
{t}: Add {c}.
{t}: Add {b} if there is a counter on Necromancer's Siphon.
{t}, remove all counters: Add {b} and lose 1
life for each charge counter removed from Necromancer's Siphon.