Sheldon the Sensual Sea Serpent, aka Sheldon, is an enemy of the Ninja Turtles. He is an alien sea creature from Dimension X, who acts as an underwater guardian for The Kraang. Sheldon the Sensual Sea Serpent debuts in Karai's Vendetta.
- He has a crush on the Turtle Sub, since he thinks that the Turtle Sub is an actual sea monster like him.
- His name was never revealed, but the producers of the show released this name for him.
- Sheldon resembles the mythical Loch Ness Monster (Nessie).
- In Journey to the Center of Mikey's Mind, he was seen inside of Mikey's Imagination flying around.