Delve (Each card you exile from your graveyard while casting this spell pays for.)
Look at the top seven cards of your library. Put two of them into your hand and the rest on the bottom of your library in any order.
9/20/2014 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.
9/20/2014 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.
9/20/2014 You can’t exile cards to pay for the colored mana requirements of a spell with delve.
9/20/2014 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.
9/20/2014 Because delve isn’t an alternative cost, it can be used in conjunction with alternative costs.