Splounder

Splounders are enemies that first appear in Super Mario 3D World. They are present in every Plessie-themed level, with the exception of Deepwater Dungeon. A Splounder can either be stationary or move side to side. They can be defeated by any attack, and will be stunned if Plessie bumps into them. Jumping on a Splounder can provide a very decent bounce, and can sometimes even lead to Plessie reaching previously inaccessible areas.

Trivia

 * Their name is a pun on Flounder, which is a fish in real life.