Ouroburos

The final stage of a leviathan is the stuff of legends. Stretching anywhere between 75 and 300 feet, this is often mistaken for a Great Wyrm. Also known as the World Snake, very little is known of them. They are extremely rare: very few leviathans ever reach this stage, nor does anyone know why only some leviathans become them.

They are generally asleep, curled into a circle at the bottom of the lake. Pity the fool that wakes one...

An Ouroburos is using:
<held in offhand>  (Magical) (Humming) a Leviathan Scale