Invocation of Pain

Convoke
When you cast this spell, sacrifice every creature
that convoked it.
Search your library for a card with mana value
X or less, where X is the number of creatures
that died this turn, reveal it, put it into your
hand, then shuffle.
If this spell was convoked, destroy target
creature with mana value X or less, where
X is the number of creatures that died
this turn.