Sea Slug

The Sea Slug is a Mysterious Being that was captured by the Hero Association. It appears in the Volume 8 Omake.

Appearence
The Sea Slug's appearance is based on a real-life sea slug.

Omake (Volume 8)
Sea Slug is in a prisoner transport vehicle and asks the other monsters if they know where they're being taken. It is shocked when Tongue Stretcher boasts about being captured by the world's strongest man King.

Abilities and Powers
Not much is known about Sea Slug's abilities, but considering it was being transported in a vehicle for low levels monsters, it can be assumed that it is fairly weak.