Under Moles are a collective boss in Castlevania: The Adventure. They are little creatures with long arms and no facial or body features which barely resemble moles. Their hands and feet lack fingers and instead end in big claw-like shapes.
A whole group of Under Moles must be faced as a boss fight at the end of Stage 2, the Caverns. There are twenty of them in total, which must be defeated in order to continue to the next level. They are initially hidden inside four holes on the wall and periodically leap out from them, doing somersaults and attempting to overwhelm the player with their vicious claws.
They hide in holes in groups and attack with swift movements and sharp claws. They don't have noticeable eyes, but their sense of smell is highly developed.
The Under Mole resembles a Hunchback in the way it curls its body.
The Rats from the sequel, Castlevania II: Belmont's Revenge, apparently took the role of the Under Moles, to the point that they're initially hidden and come out from holes on the walls, as well as attacking by leaping at the player, although now appearing as lesser enemies instead of a boss fight.