General terms:
* Antagonist: This is the most common and general term for a character who opposes the protagonist and causes trouble.
* Villain: This term is similar to antagonist but implies a more morally reprehensible character.
* Conflict: This term refers to the struggle or clash between opposing forces, which often arises from the actions of the troublemaker.
* Catalyst: This term refers to the event or person that sets the plot in motion, often by introducing conflict or tension.
More specific terms:
* Faustian bargain: This refers to a deal with a supernatural being that brings temporary gain but ultimately leads to ruin.
* Temptation: This can be a person, object, or situation that tempts the protagonist to act against their better judgment.
* Foil: This term refers to a character who contrasts with the protagonist and highlights their qualities. This can be used to create conflict if the foil is antagonistic.
* Obstacle: This is a more neutral term for anything that hinders the protagonist's progress, whether it's a person, object, or situation.
Ultimately, the best term to use will depend on the specific context of the novel.