Superstitious Schoolmaster

Whenever one or more counters are put on a
creature you control, you may instead put that
many -1/-1 counters on Superstitious
Schoolmaster.

Sacrifice Superstitious Schoolmaster: search
your deck for a spirit or specter card with
equal or lesser mana value than the number of
counters on Superstitious Schoolmaster. You
may cast that card without paying its mana
cost.