A Betta (Traditional) merman.

Bettas are fish where males intimidate and attack others entering their territory; they were once kept for the sport of fighting. Also known as fighting fish.

A Red Lionfish merman.

Red Lionfish are recognized by beautiful vertical stripes. They have venomous spines on their dorsal and tail fins; being stung causes intense pain and swelling. They are nocturnal.

An Orca merman.

Orcas are called the rulers of the sea. They have no natural predators and are extremely intelligent marine mammals. They are known to eat Great White Sharks and interact or travel between different orca groups. Whether it's a seal, a shark, or sometimes a whale, they will hunt if they judge it beneficial. Even Great White Sharks are said to flee from them.

An Atlantic Sea Nettle merman.

Atlantic Sea Nettles are known as "sea nettles of the Atlantic." While their venom isn't usually fatal, it can cause symptoms like vascular insufficiency or isolated neuritis. They are almost invisible underwater and hard to avoid, making encounters in the sea quite dangerous.