"Why are you even trying to stop me anymore? Your efforts will be in vain. You fail to realize, that for me... This is just the beginning. But for you... It's Game Over."

Bête Noire was a construct of a spell and a physical incarnation of the SOUL Trait Fear, created by Agate Lightvale solely to ensure humans and monsters would never live in peace. A thousand years after her creation, monsters were freed from the Underground and lived in harmony with humans, so Bête, under the alias Betty, met Frisk and posed as an ally. During her temporary acquaintance with Jessica Grey, they both were responsible for framing Papyrus and the murder of Sans. After Bête's true nature was revealed, her actions started expanding into a war, where she ruthlessly slaughtered humans and monsters alike to obtain their SOULs. Bête began losing track of her mind when she was enhanced with HATE, but nonetheless, Bête continued her murderous attacks on Determino, fighting her enemies physically and emotionally.