Milil is a divine entity encountered in the Epilogue. He is a dour bard who plays a Lute and supplements his music with a band of spiritual instruments.
Milil is a minor deity of song, who had been cast out of Faerûn's pantheon and banished to the Fugue Plane by Cyric. Withers pulled him back in order to "honour the worthy" with his songs.
The player character may pass a passive Religioncheck during conversation to recognize him, greatly improving his spirits. Alternatively, the player character can pretend to recognize him by passing a DC 18 Deceptioncheck.
He functions as a jukebox for the Epilogue celebration; talking to him allows to change the song that is playing.
Milil is immune to all damage. If attacked, he casts Vicious Mockery until the player character is nearly downed, then vanishes from the celebration entirely.
Fugue Plane by 
Religion check during conversation to recognize him, greatly improving his spirits. Alternatively, the player character can pretend to recognize him by passing a 
until the player character is nearly downed, then vanishes from the celebration entirely.
Milil's model.