Coyote Piper

Prue and Phoebe have their hands full when Piper is possessed by an evil spirit (Terra) with powers that travels as a vapor and who is intent on seeking out and possessing one of the Charmed Ones for her powers. The spirit is the created alienated girlfriend of an evil Alchemist Kierkan (Rainn Wilson) of great power on the day of her high school reunion. Fooled for a while, the three vanquish the alchemist when he tracks his fleeing gal to the manor where she uses Pipers power aided by a ruse to set up the ruthless assassination of her former lover. Piper, who was shy and lacked confidence being something of a doormat in high school undergoes a through personality transfer as the possessing spirit parties with abandon and acts in various ways to totally rewrite the memories Piper will engender to her classmates in the future. Piecing together the clues Prue and Phoebe figure out the possession, arm themselves with the Book of Shadows sourced exorcism spell which when cast by Phoebe and Prue proves insufficiently powerful with only the power of two to drive out the spirit who has taken over Piper and while at the manor also knocked Leo out for a few hours when he twigged that something was different and insisted she tell him his name. The demon fighting the two physically, triumphantly offers to leave Pipers' body the only way she knows how while she was getting her butt kicked physically, but when it turns out that sort of departure means killing Piper by stabbing her through the heart they retract their demand. However, shortly afterwards, Prue figures out a plan and knocks out the possessed Piper in a wild brawl during her reunion, drags her home and has Phoebe waken Leo; with the ready power of three spell to exorcise the spirit (which has added the alchemists powers to her own during his death) Prue ruthlessly stabs Pipers' supine body through the chest forcing the spirit to possess Leo's body. Striking a deal, the two offer to trade the spirits' possession of Leo's body for the alchemist-sourced vanquishing potion if the spirit first has Leos body heal Piper. Awoken from near death, Piper adds her powers and aids her sisters in reading the spell with the Power of Three , right after they give the potion to the spirit as promised, which drives the spirit out of Leo and vanquishes it resolving the crises, save for Piper's new found straight drinks and table-dancing, tough-talking reputation amongst her classmates.