(https://i.imgur.com/tvDOPck.png)
When attuned to the Relic on a Charm Domain Cleric, I get the following message when trying to cast spells.
(https://i.imgur.com/0dPte7d.png)
This message does not appear when attuned to other Charm Relics. Also, the Polymorph form from the relic was the default spider, and not a Nymph.