The Mind Flayer

Who is 011

Eleven also known as El (short for eleven) is a Female child born to Terry Ives. Her child was taken after birth and everyone was told to tell Eleven's aunt and nurses she miscarried, we all know she didn't though. Terry always said her baby girl Jane, would come home, she also said she had powers... she could move stuff with her mind. Psychokinesis, (also known as Telekinesis) the ability to move stuff with your mind. As we have seen in flashbacks and in other scenes (practically ever fight she was in) she can move, destroy, throw, practically anything with her mind. But when she uses her power her nose bleeds, (you could possibly use that against her by knowing she is using her "gift." We see this happen specifically when Dustin finds that his compasses were acting strange, El didn't want to go back to Hawkins Lab where she knew thats where that power was coming from. The power was coming from the gate. El didn't want to go back so she used her powers to move the compasses, Jacob figures out when they notice they have been going in circles, (she was just pretecting mike) he checks her hand and sees blood, meaning she used her powers to move the compasses as they walked.

Eleven is also capible of locating people, she located Billy just with a picture, that one life guard, and practically everyone she tried to find.
Brenner wanted to use that power.
Extend that power.
But Brenner did it wrong, he used abuse which clearly forced her to run like Eight and Eleven and possibly anyone else...