User blog comment:Mlgrsd/How could Lucifer land in this dungeon?/@comment-24834479-20170217191012

I think that the Magic egg thing severely weakened lucifer which is why it was able to expel him and so Crowley is able to contain him now. I don't know how he is in the form of Nick, maybe Crowley was tired of seeing him vessel-hop and redirected the old vessel.