I was looking through the D&D5 playtest spells, and saw the description of the Grease spell. Short version: you grease up an area, it's slippery, and any creature that enters it makes a saving throw or falls down.
It got me thinking: how would I handle that in DW? Or anything similar, like throwing a bunch of ball bearings on the floor. It's really a question of: how do you resolve a clever ploy that might work but sure isn't guaranteed to?
There's no basic move that directly applies. I suppose you could make a custom move (roll +?, 10+ they fall, 7-9 they're off balance, etc. etc.). But that's kinda boring, and I don't really want to make up a custom move like that on the fly or for just one spell.
So that leaves you with GM moves, principles, and agenda. Which pretty much boils down to "what flows from the fiction?" An orc charging down the hall hits the grease patch? Falls. A wraith floating by, no way. A kobold approaching cautiously? Maybe? Being a fan of the PCs makes me think "yes, he falls." At least for the first kobold. The others behind him would realize it was slippery and be more cautious.
Not sure what the point of this post is. Just thinking in public, I guess.