The Shadow's Plaything is a song that seems to be a warning against making a Faustian bargain with shadows. It is sung by Ele.
Although the lyrics have not been made in full, here is the small piece revealed in the story:
Meddle not with shadows, though shadows give thee power
Meddle not with shadows, for the shadow takes its fee
Meddle not with shadows, even though you think them playthings
But whilst thee plays with shadows, shadows may too play with thee!
Oh meddle not with shadows…