Alicanto
Steve Jackson Games is granted permission to use this in acknowledgement of my contribution. So is anyone else.
Mythological basis: Chilean mythology.
Description: A bird the size of a crow, whose feathers shine (literally) with the colour of whatever metal it's been eating lately. Gold tends to dominate so an alicanto that has been eating both gold and silver will look mostly golden. The glow is strong enough they don't cast a shadow, and very noticeable underground, but hard to see in even weak sunlight and sometimes effective camouflage against a light background like the sky.
Habits: Alicantos eat gold, silver and perhaps other precious metals. They are often encountered flying around temples, mines and the like, looking for food. The gold and silver aren't destroyed by their digestion - whatever the bird takes from its diet, it isn't the metal - and will be excreted as nuggets. An alicanto does not eat its own nuggets, but will eat those of others. First encounter with an alicanto may be a softly glowing bird investigating the entrance to a tunnel, that the PCs follow, or it may be a dazzling flash of feathers that swoops through a campsite at night and carries away a purse. (They can sense the presence of precious metals even within a purse.)
Characteristics (typical): ST 3, DX 13, IQ 7, MA 3 on ground and 20 flying. If molested and unable to escape an alicanto will fight with beak and talons: one attack per turn for 1-3 damage. The appearance of an alicanto in a dark space can be confusing: light seems to come from all directions and anyone trying to respond to it in the first turn of its arrival must make a 3/IQ roll or be at -4 DX.
Uses: Discarded (not plucked) feathers are valuable to makers of magic items and potions, notably dazzle gems, light sources and charms. Feathers, whether plucked or discarded, are thought by many cultures to be pretty, and are integrated into clothing as decoration. The feathers of an alicanto in good condition might be worth $200. Selling discarded feathers is difficult if the buyer can't confirm they weren't plucked but might be worth $50 apiece in the right hands. Alicantos do not thrive in captivity. Following an alicanto can be a good way to find precious metals.
Superstitions: Seeing an alicanto is said to bring good luck, perhaps wealth or a beautiful lover. Harming one is said to bring poverty and ugliness. Some scholars believe they were created by the mnoren as a joke. Others think that they are a symbiosis between an ordinary bird and a metal eating organism from a parallel Earth very different to those in which humanoids evolved. Both could be right.