Calm Fishing Boo
From the Super Mario Wiki
A C. Fishing Boo (short for Calm Fishing Boo) is an enemy found on Vibe Island in Super Princess Peach. Like other Calm enemies, Calm Fishing Boos are usually found asleep. If Princess Peach moves too fast, she might wake it up. When it does so, it will attack like a regular Fishing Boo.
According to the game's Glossary, one should "Walk by quietly when it's sleeping."