Death's Scythe
Oh. An old friend lent it to me. You know, he doesn't really ride a pale horse, but he does have three amigos, and they're just jonesin' for the Apocalypse!
Crowley: Keep it. Dean's covered. Death's own. Kills.. golly, demons and angels and reapers and rumor has it... the very thing itself.
Castiel: How did you get that?
Crowley: Hello! King of the Crossroads!
Death's Scythe
According to Alastair, he was given the Scythe by an old friend, possibly Crowley or possibly even Death himself.
Death's Scythe can kill Demons, Angels, Archangels and possibly Death himself.
4.15 Death Takes A Holiday
First appearance of the scythe and reference to Death in the series. Alastair hints that it belongs to Death and uses it to kill one of the two reapers in an attempt to break one of the 66 Seals.
5.21 Two Minutes To Midnight
Crowley gives Dean the scythe before the two go to Chicago to find Death, telling him it is believed to be capable of killing Death himself. How Crowley got it is unclear - the last time we saw the scythe, Alastair was using it to kill reapers before he was captured by angels. Armed with the scythe, Dean nervously tries to ambush Death in a Chicago pizzeria, but the handle begins to burn in Death's proximity and Dean drops it. Death thanks him for returning the scythe. it is considered unlikely the scythe would kill Death - Death can't die.
