Gravestorm

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.

From the Comprehensive Rules

• 502.67. Gravestorm
  • 502.67a Gravestorm is a triggered ability that functions on the stack. "Gravestorm" means "When you play this spell, put a copy of it onto the stack for each permanent that was put into a graveyard from play this turn. If the spell has any targets, you may choose new targets for any of the copies."
  • 502.67b If a spell has multiple instances of gravestorm, each triggers separately.