I anticipate that in the next session my players are going to encounter and interact with a Hag Eye. It is possible that they will ask whether or not they can, upon dispatching the coven it belongs to, attune to the eye to themselves.
Hag Eye. A hag coven can craft a magic item called a hag eye, which is made from a real eye coated in varnish and often fitted to a pendant or other wearable item. The hag eye is usually entrusted to a minion for safekeeping
and transport. A hag in the coven can take an action to see what the hag eye sees if the hag eye is on the same plane of existence. A hag eye has AC 10, 1 hit point, and darkvision with a radius of 60 feet. If it is destroyed, each coven member takes 3d10 psychic damage and is blinded for 24 hours.A hag coven can have only one hag eye at a time, and creating a new one requires all three members of the coven to perform a ritual. The ritual takes 1 hour, and the hags can't perform it while blinded. During the ritual, if the hags take any action other than performing the ritual, they must start over.
I was just wondering if there was any RAW answer to this? If not I expect that I will rule they cannot. The description makes no mention of other creatures using the eye, or attunement being involved – only its creation.
What about similar items such as the Night Hag's Heartstone or Soul Bag?
Best Answer
The descriptions of the hag eye and soul bag in the MM specifically reference the hags that created the items when talking about who uses the items.
Hag eye:
Soul bag:
So those items are clearly limited to the hags. But the heartstone, I think, is somewhat open to interpretation.
Heartstone:
From this, it looks like etherealness is only usable by hags, but curing diseases could theoretically work for all.
Jeremy Crawford has commented on this saying it's meant to work only for hags, but DMs can rule otherwise.
If you're looking for a way to use the stone for curing diseases, I'd refer to the 3.5e Wiki, where a heartstone is described as follows:
This would be fairly reasonable to use in 5e as well. Naturally, the specifics are down to you as DM. For example, since the saving throws buff is not an official function of the 5e heartstone (according to the MM), you might want to remove that ability from it and adjust the sale price accordingly.