Monsters based on logical fallacies

[the Jester]

A sphinx which gives the PCs an answer, then pleads for the riddle. In other words, it begs the question.

...named Trebek.

 

[Celebrim]

Love this one:

For instance, a demon straw man who magically pins a person to a tree or wall so they're vulnerable, they eviscerates them.

And this one:

The ad hominem is a doppleganger that ruins a character's reputation, until he has nowhere left to turn and becomes easy prey...

The Spirit of the Fallacy of Probabilities - Whenever a player is caught in the power of this monster's aura, whenever they require a natural 12 or better to succeed in a task, they automatically fail - because that is the most probable result. Each time the player accumulates a failure, they gain a marginalization point. When their marginalization points exceed their HD, they become cursed with insignificance and must make a Fortitude save or become inaudible, invisible and immaterial, and there allies must make a Will save or be subject to a memory modification spell that causes them to forget they exist.

The Spirit of the Masked Man Fallacy - This monster is a powerful illusionist that is able to take the form of an ally while simultaneously creating an illusion that someone or something else is a monster. Each person experiences this figment separately, so that each person is subject to the delusion that a person other than the monster is the monster.

The False Dilemma or Illicit Major Demon - This monster presents the victim with the image of two things that the person loves best, and then tells them that they must choose which they are willing to destroy. When the person chooses, the person is subjected to cursed geas that ultimately causes them to destroy that which they have chosen for destruction. However, the Illicit Major is a deceiver, and in fact has no power over the beloved things or persons save that which the person grants them by making the choice.

 

[tuxgeo]

The Misread Herring is usually summoned in great numbers, and can endure non-aquatic environments for hours.
A summoned shoal of Misread Herrings will taunt opponents, then fight weakly while backing away down the wrong path in an attempt to lead those opponents astray.

 

[Halivar]

The No True Scotsman is a plaid-wearing ruffian whose unique supernatural ability is to gain immunity to the first type attack made against it (because no true​ scotsman would suffer damage from a mere fireball!) The No True Scotsman cannot caveat his way out of subsequent attacks, however!