Secret 5 is a secret that's an electric eel.
Location[]
It's found in the Fields. From the entrance to the Terminal, use swap to go right where a rock is in the way.
Description[]
"Please visit the electric monsters' world."
Trivia[]
This is a reference to Pokemon Diamond (not to be confused with 4th gen Pokemon Diamond), a poorly translated Japanese game that made a very limited appearance in America. You would sometimes obtain phone numbers from defeating monsters, which you could use to call them to your aid. Most of the Engrish that Kuribo says directly relates to this game.
The electric eel closely resembles the creature on the cover of Pokemon Diamond.