Empty the Pits

Instant

Delve (Each card you exile from your graveyard while casting this spell pays for .)
Create X tapped 2/2 black Zombie creature tokens.

2014-09-20:
You can’t exile more cards than the generic mana requirement of a spell with delve. For example, you can’t exile more than nine cards from your graveyard to cast Dead Drop.
2014-09-20:
Because delve isn’t an alternative cost, it can be used in conjunction with alternative costs.
2014-09-20:
You can’t exile cards to pay for the colored mana requirements of a spell with delve.
2014-09-20:
The rules for delve have changed slightly since it was last in an expansion. Previously, delve reduced the cost to cast a spell. Under the current rules, you exile cards from your graveyard at the same time you pay the spell’s cost. Exiling a card this way is simply another way to pay that cost.
2014-09-20:
Delve doesn’t change a spell’s mana cost or converted mana cost. For example, Dead Drop’s converted mana cost is 10 even if you exiled three cards to cast it.