Peepa

Peepas are Boo enemies debuting in Super Mario 3D Land. They are small, white ghosts with stubby arms, black eyes with white pupils and a permanently smiling mouth which shows its two teeth. As ghostly enemies that have an appearance different from most Boos and often travel in predetermined paths, Peepas are somewhat similar to the Eeries in Super Mario World.

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 when they get too close, 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 Super Star.

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 do not hurt Mario or Luigi if they touch them, unlike the circling Peepas.

Super Mario 3D World
Peepas reappear in Super Mario 3D World. Unlike in previous games, they can be defeated by the light of a Light Box. Here, they make a unique distorted sound effect when defeated.

Super Mario Maker 2
Peepas reappear in Super Mario Maker 2, where they are placeable enemies in the Super Mario 3D World style. Much like in New Super Mario Bros. 2, they act like the Circling Boo Buddies, which are present in the other game styles.

Mario Party: Island Tour
Peepas made their Mario Party series debut in Mario Party: Island Tour. They replace Red Boos from previous games. In the minigame Get Reel, a few can be seen inhabiting the corridor, where they end up chasing Mario. They also appear in the minigames Horror Harriers and Peep a Peepa.

Mario Party 10
Peepas make an appearance in Mario Party 10 as the main obstacles in the four-player minigame Peepa Panic.

Mario Party: Star Rush
Peepas reappear in Mario Party: Star Rush. They serve as the primary obstacles in World 2-2 and World 2-3, where they masquerade as a duplicate ally. When players take them, they reveal themselves and hinder the party with their Cursed Dice Block, which rolls only 0's and -1's. Players cannot select to play as a Peepa, and they disappear after a set amount of time. They additionally appear in the minigames House of Boos and King Boo's Light Smite, where they travel in straight lines. They grab players and bring them to the beginning if players run into them.

Super Mario Party
Peepas appear in Super Mario Party as non-playable characters. When the Peepa Bell is used, a Peepa appears and chases a chosen player to take a coin from them each time they move.

Mario & Luigi: Paper Jam
Peepas were going to appear in Mario & Luigi: Paper Jam, but they were removed from the game for unknown reasons; however, the unused Peepa graphics can be found with the Boo graphics.

Super Mario-Kun
A Peepa appears in volume 46 of Super Mario-Kun. It encourages a Tail Boo to scare Mario. At the end of the chapter, the Peepa gets buried by an avalanche along with the Tail Boo, the Tail Boo's father, and the Bros.

Mario Tennis Aces
Peepas make their debut in the Mario Tennis series with Mario Tennis Aces and appear as spectators in the court Mirage Mansion.

Dr. Mario World
Peepas appear as assistants in Dr. Mario World.

Trivia
The ghost that dwells inside Box Boy in Super Mario RPG: Legend of the Seven Stars bears resemblance to a Peepa.