Afterlifestudio

Nick's little outburst on Cass gave me a sneaking suspicion and
may reveal the reason he's alive in the first place? At the end of ep
14/2 it was clear nick most likely killed his family this gives him an incentive to say yes to Lucifer and in fact show, they were working together. If this is the case it explains why for a brief second
he forgot he no longer has power without Lucifer, another hint to
this is his memories, vessels only retain memories they were in control of and if they were never granted the control they remember nothing so how would he be remembering the things we saw in his flashbacks while in the bunker? Shortly after experiencing these
visions of the past he reassures Cass by stating "I'm not him Castiel,
but you still can't look at me." now why would a person who has no real knowledge of where he is, who Castiel is, and sporadic visions
be so calm and confident as to say this? Surely a confused and broken man would say something more on the lines of "I am so sorry" or "Please stop this madness! What is happening to me!?!" this also
brings up the question as to how they convinced nick to stay there
with them, wouldn't a regular person feel better suited to be in a hospital or a mental institution. This suggests nick believed and or knew who they were and that he was possessed by the devil?
That or they're implying Sam and Castiel have god tier levels of convincing.

Afterlifestudio

Lastly, I think Michael might have given up dean for nick though that is highly unlikely, and probably not the case. What made me think this is simply how the scene of dean being "freed" was followed by nick murdering the witness to his family's murder almost like they were trying to say to us "Where could Michael be?" followed by showing us nick's face just as he performed a horrific act. Plus this would give Nick a better rule to play for those who think he's a great protagonist.