In order to find this very rare character, you must do this by order: go to Windhelm then head south, then just past Kingsgrove there will be a small section with a pond--after you turn left which then you'll be encountered by a crazy tree named the Mammoth Elder Tree. That tree, by the way, is where the Grampy the Mammoth eats and makes a Kudacohiscouscis bow (otherwise known as the Kuda bow), the strongest and most rarest bow in the game as of date.
You will then be confronted with Grampy the Mammoth and keep in mind, this is a random event, so it may only work half of the time. If found, he will shit out the Kuda bow and then you can either kill him to start the Angel quest, which will lead to the Angel transformation, or let Grampy live so you may possibly find another-- which sells very high in stores.
-Nah man, you NEED to find Grampy the Mammoth for the most MLG bow in the game, the Kuda bow!