Delve is an ability that was (so far) only printed in Future Sight, and as such most players aren’t very familiar with it. Here’s the relevant rules text for “Delve”: “As an additional cost to cast this spell, you may exile any number of cards from your graveyard. Each card exiled this way reduces the cost to cast this spell by {1}.”

In order to cast a card like Tombstalker, first it’s put onto the stack, then some combination of mana payments and cards exiled has to add up to 6 plus two black. While this process is going on, no player has priority, so if your opponent has already announced he’s casting Tombstalker, you can’t use an ability like Deathrite Shaman’s to exile cards from his graveyard and try to make him pay more mana for it. You’ll have to exile the cards before you even know whether or not your opponent is going to play Tombstalker, such as during his upkeep step.

Today’s Rules Tip written by Jen Wong