Oni

Demon Warriors appear in Beacon Hills during the latter half of Teen Wolf Season 3.

Appearance and Abilities
They wear modified shinobi shōzoku and black masks similar to Japanese Hannya mask.

The warriors appear to be made of black smoke or shadow. They can phase through solid matter and are skilled in martial arts combat.

They're eyes glow a golden-green color similar to the fireflies seen exiting the Nemeton in Anchors.

Motive
Their goal thus far has been to subdue and "tag" each of the werewolves (and Stiles) with what appears to be the number "5" behind their left ear.

Chris Argent has a broken version of their Hannya in a box in his apartment and believes they have come looking for him.