Historical Rules · 1 June 2020
Rule 721.3d
Official source text from the 1 June 2020 Rules release
If multiple replacement effects could be applied to the event of a merged permanent leaving the battlefield or being put into the new zone, applying one of those replacement effects to one of the objects affects all of the objects. If the merged permanent is a commander, it may be exempt from this rule; see rule 903.9a.