Peepa

Peepas are enemies appearing in Super Mario 3D Land and New Super Mario Bros. 2. They are small, white ghosts with stubby arms, 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 sidescroller 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. Peepas first appear in World 2's Ghost House.

Also, in World 3's Ghost House and other Ghost House based levels, Peepas carry moving yellow platforms. They appear when Mario stands on one of them. They will move along with the platform tracks if there is any. Sometimes they will tilt the platforms and also they may disappear at the end of a track, causing the platforms to disappear as well. These platform-carrying Peepas are harmless to the touch, unlike the circling Peepas.

New Super Mario Bros. U
Peepas are set to reappear in New Super Mario Bros. U.

Trivia

 * Peepas resemble Halloween "sheet ghosts", similar to Lantern Ghosts.