Doppelganger.

You just had painted a shadowy figure of yourself, and you felt it being alive somehow.

You shook it off and went to sleep, at the middle of the night you woke up to go to the bathroom and when you walked in, you didn't turn on the lights.

When you approached the mirror, you felt something behind you, a misty presence.. you noticed a black shadow behind you, staring at your eyes through the mirror.