Is a Night Hag in a coven considered CR 5 or CR 7 for the use of Polymorph?

[Vegvisir]

A night hag alone is CR 5, a night hag in a coven is considered CR 7. The polymorph spell that hags gain access to as part of a coven can turn a creature into a beast of the same Challenge as they are.

If a hag polymorphed one of her sisters, would she be limited to CR 5 beasts or CR 7 ones?

[PhantomSoul]

I'd treat it like any other case of polymorph: it's based on the target level/CR. That means that if you're counting that target-hag-in-a-coven as being CR 7 (like you hypothetically balanced the encounter using), then you can polymorph that target-hag-in-a-coven into CR 7 or below.

[Unoriginal]

Being in a coven increases the power of each individual Hag, so their CR would be 7 for Polymorph too.

[Vegvisir]

I appreciate the responses. If this were an encounter that I was building that was a using the coven balanced against the PCs, then CR 7 would probably be the limitation to use. However...

In this instance, it's a brief dip into Ravenloft and there is no encounter balancing. That being the case, I'm planning on sticking to CR 5 for the polymorph. Bumping the CR up to 7 doesn't add too much. In the core beasts that's just a mammoth and a giant ape, neither of which is a great fit for the setting.

I think I'll use the hulking crab from Storm King's Thunder if I want to polymorph one of the hags into a beast for melee. That should be powerful enough and not seem too out of place in the marshes.

If the party is lucky, they can forestall the confrontation with the hags pursuing them until they get to Argynvostholt where the revenants will attack the hags, and they can avoid being singled out.