Peepa

Peepas are enemies appearing in Super Mario 3D Land. They're small, white Boos with stubby arms. Peepas have black eyes with white pupils and a permanently smiling mouth which shows its two teeth.

Super Mario 3D Land
Peepas are exclusive to the Ghost Houses found in the game. These enemies are usually found alongside Boos. Peepas do not directly attack Mario or Luigi, but rather stay in a stationary position or moving in a set area, making them more of an obstacle rather than an enemy. Sometimes, several Peepas encircle a select area similar to the Octoboos in Super Mario Galaxy 2. A Peepa can only be defeated by running into it while under the effects of a Starman.

New Super Mario Bros. 2
Peepas made their next appearance in New Super Mario Bros. 2, marking their first 2D appearance. They act like the Circling Boo Buddies of New Super Mario Bros. Wii and Super Mario World. Like most Boos of the game, they have a bluish complexion.

Trivia

 * Peepas bear a slight resemblance to Eeries.