What happens if Mirrorhall Mimic copies a transforming creature?

Question

Mirrorhall Mimic is a transforming double-faced card added in the new set that copies a creature as it enters the battlefield.

Unlike previous clones, that weren't physically on double-faced cards, if this copies a transforming creature (e.g. a werewolf), it's able to transform because it actually is a transforming DFC.

Rule 712.5 seems to be relevant here:

712.5. Only permanents represented by transforming double-faced cards can transform. (See rule 701.28, “Transform.”) If a spell or ability instructs a player to transform any permanent that isn’t represented by a transforming double-faced card, nothing happens.

And the following example given leads me to believe a certain outcome applies:

Example: A player casts Cytoshape, causing a Kruin Outlaw (the front face of a transforming double-faced card) to become a copy of Elite Vanguard (a 2/1 Human Soldier creature) until end of turn. The player then casts Moonmist, which reads, in part, “Transform all Humans.” Because the copy of Elite Vanguard is a transforming double-faced card, it will transform. The resulting permanent will have its back face up, but it will still be a copy of Elite Vanguard that turn.

I think the first of these possible scenarios has to be correct:

1. The physical Mirrorhall Mimic card will transform whenever relevant, but the replacement copy effect still applies, and so it retains the properties of whatever it copied.
2. The Mirrorhall Mimic will transform and have the properties of its back face, but becomes an aura and so is put into the graveyard as a state-based action.
3. The Mirrorhall Mimic can't transform as it doesn't have the matching back face for what it's copying (I don't believe the rules support this.

Is this right?

Answer 1

#1 is almost correct, except for one small detail: you wrote "the replacement copy effect still applies"; the replacement effect was only applied once, and the thing that still applies is a continuous effect.

Answer 2

If Mirrorhall Mimic copies a creature capable of transforming, whether through a triggered or activated ability, it may transform. This follows from 702.145b and and 712.5, for how a card transforms and detailing that only permanents represented by a transforming double faced card can transform.

The Mirrorhall Mimic copies all characteristics of the active face of the transforming cards, detailed by 707.8, 712.4c, and 712.4d. This includes the ability that would effect the transformation.

In the general sense, if Mirrorhall Mimic copies a creature capable of transforming, it can be transformed into Ghastly Mimicry. This is a departure from preceding Clone-esque creatures that could not transform because they were not represented by transforming cards.

Note, Glasspool Mimic is not a transforming card, but a modal double faced card.

The deviation is if Mirrorhall Mimic copied a Nightbound creature. The triggered abilities for Nightbound, 702.145e, specifically check if the permanent is back face up.

702.145e Nightbound is found on the back faces of some transforming double-faced cards and represents two static abilities. “Nightbound” means “As it becomes day, if this permanent is back face up, transform it” and “This permanent can’t be transformed except by its nightbound ability.”

Despite Mirrorhall Mimic copying the characteristics of the Nightbound creature, it remains the Front Face of a card (712.1b).

When the Mirrorhall Mimic transforms, it will not transform into the opposite face of the permanent it copied. Instead, it will transform into the Ghastly Mimicry. Ghastly Mimic is an aura not attached to a creature, so it will be put into its owner's graveyard (704.5m).