Delve

Delve is an keyword ability, introduced in Future Sight. Delve is a static ability that functions while the spell with delve is on the stack. “Delve” means “For each generic mana in this spell’s total cost, you may exile a card from your graveyard rather than pay that mana.”

History
In Future Sight, delve was only printed on three timeshifted cards and was a cost reduction. It was re-introduced as the clan specific mechanic for the Sultai Brood in Khans of Tarkir and Fate Reforged. It also appeared in Modern Horizons and Commander 2020.

As with many cost reduction mechanics, several Delve cards were banned in various formats. While the development aspect may theoretically be solvable, the anti-linearity and environmental requirements has rendered it high on the Storm Scale.

Rulings

 * 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. (This is similar to the change made to convoke for the Magic 2015 Core Set.)
 * You can’t exile cards to pay for the colored mana requirements of a spell with delve.
 * 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.
 * Because delve isn’t an alternative cost, it can be used in conjunction with alternative costs.