“PAPA” THEORY
Dr. Martin Brenner (Papa), attacked by the demogorgon in Season 1, yet still alive in Season 2, confirmed by executive producer Shawn Levy.
Who is “Papa”?

Worked on controversial Project MKUltra in Hawkins Lab
Crazy Scientist; Wanted discovery of some power?
Loving Father; with children of his own?
Papa’s purpose in “experiments”

Why research in kids with potential powers, unless he had something to do with these experiments in the past.
Papa might have been exposed to some supernatural power and wants to know how to cope with it.
Perhaps he made a mistake in creating the giant shadow monster and wants Eleven to kill it.
Papa stages Terry Ives miscarriage to keep Eleven, basically raising her in Hawkins Lab.
Why else would he want Eleven, it only makes sense that Dr. Martin had made a horrible mistake and wants to get rid of his guilt and fix his mistake.
Instead, maybe the monster is actually himself, but not exactly himself, himself, but the upside down version of him.
For example, why is he so attracted to investigating the Upside Down World, it’s like some sort of magnetic pole bringing him towards investigating the world.
There are many Eleven theories of her being a demogorgon, but the theory Dr. Brenner Martin is the giant shadow monster who wants revenge on what Eleven and her friends have done to ruin his perfect plan makes a lot of sense as well.
The demogorgon attacks Dr. Brenner Martin and the shadow monster haunts down Eleven and her friends.
008/Kali illusion powers, Eleven’s sister

Why bring her into the storyline unless she might be returning for future seasons. Maybe Kali and Jane may be forming an alliance once a again and creating an army
Eleven is not alone, this is a huge breaking point for the show
New members for next season? New numbers, and more background stories for the show
Army of people with supernatural powers? Defeat the giant shadow monster tentacled creature in Season 3
Dr. Brenner Martin brought Eleven into the laboratory like he did Kali? Who is Kali exactly.
Well she has supernatural powers and lives with a bunch of bandits who want to kill every single scientist who worked in Hawkins Lab.

Will Papa return for the next season or perhaps a new crazy villain will be added to the show? But if he does what do you guys think is going to happen?
What do you think is going to happen in Season 3 of stranger things?
Comment down below what you believe.