Gravestorm is a triggered keyword ability. It's similar to storm, except that instead of counting the number of spells played that turn, it counts the number of permanents put into a graveyard from play that turn. Gravestorm was introduced in Future Sight. It has only been printed on one card so far, the timeshifted Bitter Ordeal.
From the Comprehensive Rules:
- 702.68. Gravestorm
- 702.68a Gravestorm is a triggered ability that functions on the stack. "Gravestorm" means "When you cast this spell, put a copy of it onto the stack for each permanent that was put into a graveyard from battlefield this turn. If the spell has any targets, you may choose new targets for any of the copies."
- 702.68b If a spell has multiple instances of gravestorm, each triggers separately.
- Bitter Ordeal -
Search target player's library for a card and exile it. Then that player shuffles his or her library.
Gravestorm (When you cast this spell, copy it for each permanent put into a graveyard this turn. You may choose new targets for the copies.)