Bonnie uses an "Expression triangle"—fueled by the deaths of 12 hybrids, 12 humans, and 12 witches—to drop the veil between the living and the dead. This allows ghosts to temporarily manifest in Mystic Falls. Reunions and Revenge:
The original vampire Kol returns seeking revenge on Elena and Bonnie. [S4E22] The Walking Dead
Silas uses his psychic powers to torment the group, specifically making Caroline hallucinate that she is cutting herself. Bonnie eventually uses Expression to turn Silas’s body into stone, though he remains a threat if he receives even a drop of blood. Character Arcs Bonnie uses an "Expression triangle"—fueled by the deaths
Elena Gilbert, still struggling with her humanity and grief over Jeremy’s death, seeks revenge against Katherine Pierce. Key Plot Developments Silas uses his psychic powers to torment the
Stefan’s best friend Lexi returns, providing emotional support and suggesting that his romantic chapter with Elena is truly over.