You probably guessed the question: if Ixalan's Binding targets a mutated creature, does its ability apply to all creatures mutated together since they each get exiled with it?
Certainly.
From Lair of Behemoths' Release Notes: If a merged creature leaves the battlefield, one object leaves the battlefield and each card is put into the appropriate zone. For example, if a merged creature containing three cards dies, one creature died and three cards were put into a player’s graveyard.
From Lair of Behemoths' Release Notes:
If a merged creature leaves the battlefield, one object leaves the battlefield and each card is put into the appropriate zone. For example, if a merged creature containing three cards dies, one creature died and three cards were put into a player’s graveyard.
https://magic.wizards.com/en/articles/archive/feature/ikoria-lair-behemoths-and-commander-2020-edition-release-notes-2020-04-10
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules