How messy is your messy?
It’s one of the more open-ended tags in the game, and it’s applied to monsters ranging from the Apocalypse Dragon to the humble Cave Rat. Do you ramp into it with soft moves like NPC slaughter, environmental destruction, or just a description of how nasty those teeth look? Do you pull it out as a surprise to emphasize how sudden things can go south? Do you start small and ease into the devastation (degrade armor -> break armor -> sorry about your legs)?
I don’t like starting thought discussions like this with my personal anecdotes, but I was struck by it when I threw some sahuagin at my PCs last session and was confronted with the combined might of messy and one of their main attacks being “bite off a limb.” To a certain extent it mirrors the old issue with using fumble rules in D&D — it’s fine for monsters because most only exist for one battle, but surprise PC death or disfigurement is a long-term deal. I ended up massacring & de-limb-ing some companion NPCs, playing up bleeding wounds and useless limbs, applying conditions like Weak, and relieving the Wizard of some of his fingers. But it was an interesting line to toe between respecting both the principle of “Think Dangerous” and the monster’s actual move, while also understanding that this was intended to be a harbinger of things to come rather than a TPK/PC retirement party.