My headcannon was always that they were action figures. The episode where they all go on the surface shows all of the characters as puppets
so in my head all of the characters are real items that are being animated by some sort of undersea magic.
I think the non-official canon is Bikini Bottom is near Bikini Atoll, the site of nuclear weapons testing in the Pacific Ocean. Radiation created anthropomorphic sea creatures like SpongeBob. I like your idea of Mermaid man/ Barnacle action figures… maybe irradiated ones at that.
Radiation magic, just like in Fallout!
I mean they are not human just by the fact that they can live underwater.
Mermaid Man breathes through the starfish on his nose. It’s not decorative.
Could not the squirrel be man sized. It does afterall have the ability to don underwater diving equipment
We’ve seen Sandy outside in Texas and she’s s regular sized squirrel.
