Does mutating onto a commander in the command zone work?

Mutate is a keyword that lets you cast a spell for its mutate cost, but only if the target is a non-Human creature on the battlefield. This is a core targeting restriction defined in CR 702.139b, which explicitly states the target must be a creature on the battlefield you own or share control of.

The command zone is not the battlefield. A commander sitting in the command zone is not a creature — it is a card in a zone. You cannot legally target it with a mutate spell any more than you could target a card in a graveyard or library. The zones are entirely separate game areas (CR 400.1).

Even if your commander is already on the battlefield, there is an additional important constraint: mutate only works on non-Human creatures (CR 702.139b). Many commanders are Human, which would make them illegal mutate targets even when they are on the battlefield.

Concrete example: You control Nethroi, Apex of Death (a non-Human legendary creature) on the battlefield. Your opponent casts a mutate creature targeting Nethroi — that is legal because Nethroi is a non-Human creature on the battlefield. But if Nethroi had died and been moved to the command zone, no one could mutate onto it there.

Bottom line: mutate requires an on-battlefield, non-Human creature target. The command zone categorically does not qualify, regardless of any commander-specific rules.