For those who don't know (because even I had to double-check) what poltergeist are, according to wikipedia:

"the apparent yet unexplained manifestation of multiple force reactions caused by a seemingly invisible entity. Most accounts of poltergeist manifestations involve such force being triggered at objects, usually household (destruction and relocation of furniture, levitation of cutlery, knocking on the doors), although some seem to describe accompanying hallucinations, as well as physical attacks on human witnesses. Such actions can include pinching, biting, hitting and tripping the victim, or producing sentient noises (moaning, laughing, talking etc.) without clear source.

Poltergeists occupy numerous niches in cultural folklore, and have traditionally been described as troublesome spirits who, unlike ghosts, haunt a particular person instead of a specific location. Such alleged poltergeist manifestations have been reported in many cultures and countries including the United States, Japan, Brazil, Australia, and most European nations. The earliest recorded cases date back to the 1st century."

Evidence I've seen for the theory:
- When Jackson was being controlled last season and they asked if he was there he said "us. we're all here", which makes it seem that he was referring to more than just himself and Matt since he would have said "we're BOTH here" to refer to two people.
- Jeff Davis wouldn't comment on the poltergeist theory, so it hasn't been rejected.
- The window was closing by itself behind Stiles.
- The girl tonight being tripped by nothing.
- When Isaac was in the ice bath the lights started flickering when he was recalling memories and he said "they're here, they're here."
- link

Yeah. As for me I'm absolutely lost and have no clue, though poltergeist would make sense.

Did anyone else see the teen wolf promo with the cloaked stranger chanting Latin? Here's a link. It's the fourth video.

link

I think that he's doing the sacrifices.