[RPG] What makes a creature Aberrant

There are items that have powers and properties that look for fey origin:

• Cold Iron Bracers grant a defense bonus against fey creature's attacks.
• Cold Iron Weapons' immobilization daily power damages fey creatures.
• Fey Slaughter Weapons deal extra critical damage against fey creatures.

I can't think of any feats that require "fey" but I could imagine such.

I can't think of any monsters that have powers (or class powers) that look for fey, but again I could imagine such.

There's an episode of the 1970s Kolchak: Night Stalker series that includes a shapeshifter called a rakshasa. It also involves a vulnerability to blessed crossbow bolts/piercing weapons, which isn't part of Hindu tradition (I think Ravana, greatest of the rakshasas, was actually killed by a round thrown weapon called an asthra). Here's a summary of the episode.

Gygax confirmed the inspiration in a forum Q&A post in 2005:

I was a fan of Kolchack, the Night Stalker, when it first aired, and sure enough they had a rakshasa as a monstrous evil on that show. I liked the idea of the demon being destroyed by a blessed wooden crossbow bolt, that being akin to the stake through a vampire's heart, so I went with that in the MM.

Nowadays I'd be less prone to allowing so easy an answer to the threat of a rakshasa, although not many adventuring parties are equipped with a crossbow and blessed bolts.

Cheers,

Gary