I hope that the Fey'ri on Arelith comes to represent the stats shown in Races of Faerun. Now that class is locked behind an application, providing their IC lore powers is something I believe should be implemented.
One of the defining features of the class is being able to shift into any humanoid form (per Races of Faeurn also mentioned in Cloak and Dagger) one Fey’ri even extended this ability and was able to become a doppelganger and posed as one. I do not believe the extreme would fit Arelith
Something that could work is taking the form of a human or a half-half. Disguise race being unlocked for them not requiring Bluff or Perform as this is their racial power. Breaking the disguise could also work the same as others not revealing the true name only that the person is Polymorphed.
Current rules keep the disguised Fey’ri in check as under the rules posted on Astlobe all that is required to ban someone in disguise is to cut off the ear, record what happens, and request a scene with the NPC to ban the disguised person.
Other powers not implemented is the Fey’ri powers. Darkness is one of the powers Fey’ri may have, and another is charm. There are a variety of other spell-like abilities in their arsenal Fey’ri are supposed to be able to choose four of them unless they take a powerful one (darkness is not one of the four). According to the Races of Faerun due to their fiendish blood fey’ri do not all get the same powers. This makes all Fey’ri having darkness contradicts to the Races of Faerun.