Book about Dungeon monsters and their lives.

I came across a Reddit post a while back about a book about the monsters who live in a dungeon and their lives. Dungeon living from their point of view. Unfortunately if you google anything dungeon and monsters all you get are A ton of D&d links.

It had the normal monsters Liches undead and such but what seem to stand out and what I remember was the demon of the story was not in his final form. I believe the writing was satire in nature hope this helps sorry if it's not enough to go on.