Pinkie Pie is killed in an explosion at a new alchemy lab in Canterlot she was touring with Mane Six. Several months later a mysterious villain begins plaguing Equestria with increasingly lethal attacks based on jokes, parties, pranks and laughter, leaving their victims face frozen with rictus grins or disfigured faces with crooked smiles carved into their mouths. After the villain reveals herself, the press dubs her the Clown Princess of Crime, The Hateful Harlequin, The Mare Who Laughs. Shortly after her first attack, the Princesses contact a wanted vigilante, an enigmatic and dour unicorn detective known as Monochrome. They give him juriceprudence to discover who this new villain is and bring her to justice, at any cost.

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This is an alternate universe story placed before Twilight Sparkle becomes an alicorn.

Mature content warning for acts of terrorism, disfigurement, sexual assault, mass murder, arson and general non-pleasant things.

Thank to The_Darker_Fonts for the edit and mmfmlpl. (much motherfuckin' my little pony love)