Mary undergoes intense mental torture. By the end of the episode, her brainwashing is seemingly complete when she is ordered to kill a fellow hunter and friend.
Crowley’s attempt to keep Lucifer under his control fails. Lucifer manages to reverse the security system in his vessel, overpowering Crowley and escaping his confinement. [S12E21] There's Something About Mary
The British Men of Letters use a "bug" (a tracking/listening device) to locate and eliminate American hunters. Sam and Dean eventually find the bug in the Impala. Mary undergoes intense mental torture