454895 represents a chemical or reagent that can force a leviathan from its human host; trick is that they must be contained & forced back into Purgatory quickly in order to prevent them from attaining a new one, & only He Who Is Like God can pull it off in God’s absence. Sam is informed of this by Lucifer, who isn’t a hallucination; he is communicating directly w/ Sam from w/in the Cage due to a link between Sam’s soul and his grace. Sam rebels at the notion, but Lucifer promises that he won’t try to possess Sam again & will even help rid the planet of leviathans b/c he certainly isn’t letting those guys destroy the planet; if Luci doesn’t get to, nobody does. With Crowley’s help, the boys get the rings & open the Cage back up, releasing Lucifer & Michael; Michael is wearing Adam, Lucifer exits quickly to locate a vessel. This gets the alpha’s attn, who reveals himself after Dick is forced from his host & trapped. Michael & Luci sense Cas in there, but they can’t smite the leviathan w/o hurting Cas, which Dean won’t allow. He banishes the angels before they can try. Sam, catching the backlash due to the grace link, is out cold. Dean is alone w/ Levia!Cas, who mocks him w/ Cas’ feelings for him & taunts that Dean doesn’t have what it takes to destroy him. In a surprise move, Dean rams the sprayer w/ the reagent into Levi!Cas’ mouth & blasts him w/ the stuff. He watches those eyes go from surprised to panicky to begging & finally lifeless as the leviathan is forced out. Michael returns, sees Dean cradling Cas’ body to the ground, & deals w/ the leviathan. “Now you understand the true cost of what I must do in killing Lucifer,” Michael tells him. Dean grates out “I wasn’t killing Cas; I killed the thing that killed him. If you can’t tell the difference, you’re dumber than you look.”