The end is here! Sam has the idea of saying yes to Lucifer so that he can get him into his cage, now that they have the horsemen's rings. But, everyone is aware, he probably won't come back out. Can Dean live with that? And will it even work? Sam and Dean come face to face with Lucifer and must make some "heartbreaking decisions."
Luckily, in RL, we know the boys will be back in season six!
Dean - "No. That's the thing. It's not on me to let you do anything. You're a grown - well, overgrown - man. If this is what you want, I'll back your play."
Dean (about Lucifer) - "Maybe this is him rolling out the red carpet. Maybe he knows something we don't."
Sam - "Dean, I'm sure he knows a buttload that we don't. We just gotta hope he doesn't know about the rings."
The title "Swan Song" is a reference to an ancient belief that the Mute Swan (Cygnus olor) doesn't sing in its lifetime until the moment just before it dies, when it sings one beautiful song. The term swan song has become an idiom for any performance or accomplishment that someone knows will be the last and puts all of his effort into.
Swan Song Records is the record label founded by Led Zeppelin.
Lucifer says to Sam, "I'll bet a fiddle of gold against your soul just to say I'm better than you." This is in reference to the Charlie Daniels song "The Devil Went Down to Georgia."