Complex sentence: Barnacle Boy, who in the episode "Mermaid Man and Barnacle Boy V", changes his name to Barnacle Man, (not permantly) in Mermaid Man and Barnacle Boy VI, he is Barnacle Boy again.
Split into simpler sentences: Barnacle Boy, who in the episode "Mermaid Man and Barnacle Boy V", changes his name to Barnacle Man. This was not a permanent change; in Mermaid Man and Barnacle Boy VI, he is Barnacle Boy again.