Peepa

Peepas are enemies of the Boo race, that first appeared in Super Mario 3D Land as enemies in Ghost Houses. Their latest appearance in the Mario series is Super Mario 3D World. They are white ghosts, with stubby arms, and permanent smiling face, and black eyes with white pupils.

Super Mario 3D Land
Peepas appear in Super Mario 3D Land, marking their first video game appearance, found in Ghost Houses, they don't make any physical attack when Mario (or Luigi) is near, so they appear as an obstacle instead of a enemy, the only way to defeat them is being Invincible Mario (or Luigi).