Seeno Evils (or Miteminufuri) are creatures that appear within the dream world of Wonder Egg Priority. They appear as small child-sized beings in black suits. All of them wear identical red masks, carry kitchen knives, and giggle incessently. They relentlessly chase the people that hatch out of Wonder Eggs in order to harm them.

The Seeno Evils are seemingly able to track the Wonder Egg people, regardless of walls or distance. They leave paint-like splotches on every surface they pass by, and a creaking door sound is heard each time they appear. They move by bouncing in large groups, and are able to do so at considerable speed in order to chase their prey. They appear to obey Wonder Killers.
Despite their unnerving appearance, they can be destroyed quite easily, with a single hit from a magical weapon (such as the pen Ai wields).Seeno Evils are able to transform into a "Hater".

(Source: Wonder Egg Priority Fandom Wiki)