I was fighting the mimic with a friend when the first time teleport happened. I went to phase 2, my friend stayed at phase 1. The phase 1 mimic was gone. however the phase 2 mimic was with me. I ended up dying to it. after a bit the mimic hopped off screen (over to the phase 1 area..nice method of time travel btw) and my friend killed it. I was transported to phase 3, still a ghost, while my friend was not. This obviously prevented us from (dying) beating the boss, forcing a reset.
Included images of my and friends view. (friend's view is post phase 2 defeat)
Included images of my and friends view. (friend's view is post phase 2 defeat)