This is gonna be a long one.



Born into poverty under the thralls of an alcoholic thief, fate fell upon Trixie when the Sparkle family took her in when her father died. Desiring power, she initially made Twilight's life a living hell and slowly displaced her as a worthy heir of the Sparkle fortune, but a heated confrontation with Twilight convinced Trixie to stand down.



Seven years pass, and Trixie's animosity seems to disappear. But Twilight discovers that Trixie has been poisoning her mother, and goes to find a cure and bring in the police. While Twilight is away, Trixie falls into alcoholism and despair, her plans unwound and her life seemingly over...



Until she discovers the secret of an old Sparkle heirloom, the Alicorn Amulet; When splashed with blood, the amulet turns its wearer into a vampire.



Trixie rejects her equinity, burning down the Sparkle mansion and going on a killing spree across Equestria, killing and zombifying as many ponies as possible. But Twilight, who has trained in the magic of Harmony, fires a stoning spell that blasts Trixie off a tower.



Before the spell completely petrifies her, Trixie cuts off her head and realizes she needs a body. So she sneaks aboard a cruise ship on Twilights's honeymoon, surprise attacks and kills her, and used her vampire regenerative powers to affix herself on Twilight's neck.