Historical Rules · 8 September 2022
Rule 608.3b
Official source text from the 8 September 2022 Rules release
If the object that’s resolving has a target, it checks whether the target is still legal, as described in 608.2b. If a spell with an illegal target is a bestowed Aura spell (see rule 702.103e) or a mutating creature spell (see rule 702.140b), it becomes a creature spell and will resolve as described in rule 608.3a. Otherwise, the spell doesn’t resolve. It is removed from the stack and put into its owner’s graveyard.