Ruby's Knife

Ruby with her demon-killing knife in 3.01 The Magnificent Seven

• In 3.01 The Magnificent Seven, Ruby appears during the battle with the Seven Deadly Sins, and kills three of the demons with a dagger. Until this point, the only way to get rid of a demon had been exorcism, which sent it back to hell, or with the Colt which killed it.
• Bobby states that he has never heard of a blade that could kill demons.
• In 3.09 Malleus Maleficarum, Ruby tries to use the knife to kill Tammi but loses it in the ensuing fight. Dean eventually kills Tammi with it.
• In 3.16 No Rest For The Wicked, Dean steals the knife in the hope of using it against Lilith. However when Sam attacks her with it, she stops him with her powers. Later, after Dean has been killed, Sam is able to withstand her power,and is about to use the knife on her when she vacates the boddy she is using and escapes.

Other information:

Ruby possesses a mysterious and somewhat magical "demon-killing" dagger. It has been seen and utilized many times throughout the season, mainly as an instrument to kill demons. Upon being stabbed by the dagger, both the demon and human host suffer immediate death. The demon possessing the human is shown to convulse violently, as if shot with the Colt. It then flickers with light before expelling a small cloud of smoke from the human body, leaving whoever it was possessing dead. The demon possessing the body then also disperses, as the dagger's effects mirror that of the Colt. However, both its creation and how exactly it can kill demons has not yet been revealed. Ruby's dagger was featured prominently in the season three finale, "No Rest For The Wicked," and is currently in Sam's possession.