Historical Rules · 22 July 2016
Rule 702.68a
Official source text from the 22 July 2016 Rules release
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 the battlefield this turn. If the spell has any targets, you may choose new targets for any of the copies.”