Peekaboo, known as Nainai (ナイナイ) in Japan, is an EM Virus appearing in the Mega Man Star Force series. They look like large grey ghosts with their hands covering their faces. When they do show their face, it lets out a sonic wave, the "Ghost Pulse". They also have faces on their hands, but these hands are much happier than the actual face. When Peekaboo reveals his mouth, a small cannon can be see.
Another version is the Wavyboo. The Wavyboo is green and has higher health.
Wavyboo HP: 130
Ghost Pulse (ゴーストパルス) Battle Card.