Throughout the Scholomance Academy  Cinematic trailer there is actually a clearly defined student that you see throughout the whole trailer

First he gets drenched in the wave scene (and is clearly  on the ground right before that)

Next  he makes a hairy mustache spell and mocks another student.

Then he mentions "Corpses" in the academy yard and gets a sheep head

Later we seen him cheering on a Demon Hunter student only to get pulled down into a dark room,  and probably got his soul stolen.

Also he is in a bubble in the thumbnail.