Enforced: "We haven't really hammered out how the monster works, so let's just have it follow no rules to make it scarier."
Lampshaded: "Why can't monsters from outside reality ever just adhere to laws of physics or maybe just common sense!?"
Invoked: Character tries to create or fake an incomprehensible monster.
Exploited: Character creates or fakes an incomprehensible monster to benefit themselves.
Defied: A hard to comprehend creature strives to make itself understandable.
Discussed: "There are no words to describe the sight before me. Such things shouldn't exist. Will I ever sleep again? Will I be given the chance to try?"
Bob: You can't really have an incomprehensible monster in a work of fiction. I mean you can't describe something you can't comprehend.
Alice: Well what about Uhluthc in Mad Mountains? He was pretty freaky.
Implied: There are many tales of the incomprehensible monster, and solid evidence to support it's existence, but the heroes haven't encountered it and word of mouth can't agree on a description - or describe the monster at all.