Lurking Leechwyrm

Delve (Each card you exile from your graveyard
while casting this spell pays for {1}.)
When Lurking Leechwyrm enters the battlefield,
put X -1/-1 counters on it, where X is the
number of cards exiled to cast this spell.
Whenever Lurking Leechwyrm attacks, you may
move a -1/-1 counter from it to target creature
an opponent controls.