Erato

In the Sanctum's central courtyard there is a great round bathing pool of dragon-make, deep enough for a grown guardian to submerge themselves. It was doubtless beautiful once; clear water and sun-warmed stone by day, a silver mirror to catch the moonlight by night. Now the liquid within is murky and overgrown. Covered with duckweed and algal sludge, choked by mud and fish eggs and lotus roots. It is here that Erato makes her home.

She is an ancient thing in her own right, though long diverged from the Icewarden's first children. She speaks a forgotten tongue that not even Idris knows (despite his very unsuccessful attempts to get her to teach him). But her lack of ability to communicate with the Sanctum's residents doesn't bother her in the least. She prefers simple pleasures: sunbathing, swimming, catching fish for her meals, and lunging out of the water to snap at any unsuspecting soul who comes too close to her pond like an incredibly hairy, antlered crocodile.

These displays are followed by a deep rumbling sound that seems to be Erato's version of chuckling...and she hasn't actually eaten anybody. Not recently, anyway.

She's a good swamp creature.