|Dates||???? - 2015 (killed by Dean Winchester)|
|Episode(s)|| 10.21 Dark Dynasty|
10.22 The Prisoner
You know, in the old country, they'd make you eat your first heart. But... I like to think we're a little more civilized.
– Monroe Styne, 10.22 The Prisoner
In Shreveport, Louisiana Eldon Styne is getting chewed out by his father Monroe for being unprofessional and leaving a body and witnesses. Monroe threatens to turn his son into a lab rat unless he redeems himself by cleaning up his mess in Omaha and then tracking down he Winchesters. When Eli questions his uncle giving such important tasks, given his questionable judgment. Monroe brings up Eli's own issues, like having shirked his duties in tracking down Charlie Bradbury, a task that was passed on to him after Jacob's death. He orders Eli to report in with Eldon and back his effort before dismissing him.
Monroe is washing up and admonishing Eldon for his failure in killing the Winchesters and getting back the Book of the Damned. But when Eldon tells his father about the Bunker, and his plan to take some men and raid it for its contents, Monroe believes it is a good idea, and that Eldon will need a new arm. Monroe has Eli summon his youngest son Cyrus to the operating room, Monroe tells Cyrus that it's time for him to harvest his first body and unveils the bully who had been harassing Cyrus earlier. When Cyrus refuses, Monroe threatens him by telling his son that he will butcher the bully himself and then place Cyrus on the table to be modified. Monroe takes his son's hand and places a scalpel in it, and guides his hand as the blade cuts in the bully's chest. After the body had been harvested, and Eldon given a new arm, Monroe congratulates his son and allows Eldon and Roscoe to take Cyrus along to the Bunker.
When Dean makes it to the Styne Estate, he is surprised to see that Monroe had been prepared for his arrival with heavily armed men waiting in the home. After Eli knocks Dean out, Monroe had him taken to their operating room to be harvested for parts. While Dean tries to explain that the Mark of Cain won't allow him to die, will turn him into a demon, and everyone will die. Monroe believes Dean to have made a compelling case, however the thought of a man that doesn't die offers up a too perfect lab rat opportunity, and decides to proceed with the harvest. As Monroe is about to slice into Dean, Dean is able to get free and knocks Monroe down, and proceeds to kill Eli and the nurse assisting them. As Monroe is crawling to the door to try and not to gain his attention, Dean grabs a hold of him and drives him head first into the steel door before placing him in a headlock. Monroe tries to tell Dean that his home and family are about to be destroyed, but is unable to finish before he is rendered unconscious from his neck being strangled and snapped by Dean.