The acorn monster is a monster who appears in the Halloween special "The Legend of Boo-Kini Bottom."
The acorn monster is a wooden robot created by Sandy. Its head is shaped like an acorn. It has yellow light bulbs with black pupils to make it look like eyes, and its mouth has two sharp, white teeth. Its body is made to look like a tree stump and its body and limbs dark brown.
- As seen when the acorn monster falls apart, it is filled with acorns.
- It is a parody of Frankenstein's monster.
- It has strings on it like a puppet.