Here is the full list of all 14 THOTH achievements.
Beat four sets of levels
Beat the first set of levels
Beat eight sets of levels
Beat twelve sets of levels
Finish the main game
Beat the set of 8 procedurally generated levels
Beat the set of 16 procedurally generated levels
Beat the first lava challenge
Beat the final challenge
Beat 16 levels in a row in single player
Beat 32 levels in a row in coop
Beat the 64 normal levels in one sitting, alone, while in coop-mode (other player must not move or help)
Beat the first inverted challenge
Beat the final inverted challenge