Faeling in warrior guilds who take the specialisation of moon or stag will take on the specialisation race of "Pictsie". They will gain -3 size, +10 con, +10 str, lose their ability to fly, and they will become immune to the effects of alcohol poisoning. They will also turn blue, with red hair.

...How much have you had to drink tonight? Alright, Laysus, we're cutting you off. Come on, I'll walk you home.

You forgot the most important part: if they encounter a cow while with three or more other Pictsies, they are forced to steal the cow and take it to the nearest village.

NAC MAC FEEGLE! Discworld references = fun!

A movement made her turn. A small blue man wearing a blue cap was staring at her from the shelves over the washcopper. He stuck out his tongue, made a very small obscene gesture, and disappeared behind a bag of washing crystals.
"Nanny?"
"Yes, luv?"
"Are there such things as blue mice?"
"Not while you're sober, dear."
--Carpe Jugulum

You know I have several times considered putting some form of the Nac Mac Feegle in Lusternia, but I expect I would have to get permission from Terry Pratchett first.

You should be emailing him now, then