Season 3 operates under the pressure of Dean's crossroads deal — he has one year to live before hellhounds collect his soul. This ticking clock gives the season an urgency that drives both the plot and the creature encounters.
Creatures Introduced
New creatures include: changelings, the crocotta, the sin-based embodiments (the Seven Deadly Sins as demons), a new type of ghost (the death-echo), and Ruby's first appearance as a demon ally with ambiguous motives. Pagan gods were explored more directly with the winter solstice gods in "A Very Supernatural Christmas." Bela Talbot introduced the concept of a human who profits from the supernatural world by stealing and selling cursed objects.
Major Lore Developments
Ruby provided the Winchesters with her demon-killing knife, one of the show's most important weapons. Lilith was introduced as a powerful white-eyed demon and the holder of Dean's contract. The season explored the mechanics of crossroads deals more deeply, including the revelation that deals are binding contracts enforced by hellhounds with no legitimate escape clause. The season finale depicted Dean's death by hellhound and his descent into Hell — one of the show's most devastating moments.