Full Moon Man

A bigfoot/sasquatch/yeti type creature that only spawns once per full moon, and only in loaded forest chunks. It looks dark brown and hairy, although uses the villager model minus the nose.
Maybe something a half size bigger than the villager.
Perhaps it can have a light level of like 1 or 2.
Upon spawning, it'll have a howling sound that echos to hint the spawn direction, but is silent after that.

It should move silently and should despawn within minutes of being spawned.
It should have more health than Endermen and melee hit harder than zombies.
It should be a neutral mob that doesn't stop walking unless aggro'd by a player.
Its movement speed should increase after being aggro'd.
There could be an item (some kind of food, golden apple, or rabbit's foot or something)
that you can use on it like you were feeding it, and it rewards you with something special.
You get no drops for killing it, although it should give a lot of experience.

After receiving its special reward item, it slowly vanishes and despawns.
This special item could be something unique to it, or be a high end loot table of rare, harder to get items.