Barnacle Man is an alter-ego/version of Barnacle Boy seen only in the episode "Mermaid Man and Barnacle Boy V."
Barnacle Man is basically Barnacle Boy dressed in a vampire style jacket with a red shirt that has a skull-and-crossbones on it.
Barnacle Man is formed when Barnacle Boy joins the dark side after getting fed up with Mermaid Man still treating him as a little kid.
|| "Octavius Rex, a.k.a. long, tan, and handsome!"