It is a green plant monster attached to the edge of the room. It appears to have two armour plates, above and below it, around a mossy mass with three tendrils coming out.
The Mossmouth is sessile and remains on the rightmost edge of its arena for the entire fight. It uses a variety of dull green attacks, and has 180 HP.
- It is named after Derek Yu's personal game development studio, which is mostly known for Spelunky.
- There is no wall behind the Mossmouth. It is thus possible to skip the fight by walking through the boss and off the right side of the screen without defeating it, although doing so will incur contact damage.