Someone mentioned Angela being in the mirror above. It made me go back and slo-mo it to see who all popped in, and there was a surprising guest or two.
The flashes I could see:
Elliot
Tyrell (at first glance it looks like Mr. Robot but it's him, a couple of times)
Darlene
Mr. Robot
Angela
fsociety mask
...and one frame of Mr. Sam Esmail himself.
I couldn't place the face in the frame, as a character, and on a hunch went to find a photo of him, and sure enough it's Sam.
I'm not sure if it's relevant or not, but it was an interesting montage.
