Foes they can't hurt

Sometimes, the PCs can't feasibly attack their foe. The monster might have a special quality (like "made of stone") or tag (like huge) that makes them effectively invulnerable to the PCs' weapons. It might have a move (like "swat arrows from the air") that counters attacks. Fictional positioning might make an attack extra dangerous or impossible (it's got a reach weapon and the PC has a hand weapon).

When you first present such a monster, convey how hard it'll be to hurt. "It's got this lashing, whip-like tail, at least 10 feet long." "It's like literally a moving tree, 30 feet tall and made of wood." "She moves with the calm confidence of a master fighter."

If the players say that they attack in a way that just wouldn't work, then they don't trigger Clash or Let Fly. Instead, tell them the requirements ("you'll have to get past that tail first") or reveal an unwelcome truth ("you chop into it full-strength, and it just, like, takes a chip out of it") or put them in a spot ("she side-steps like it's nothing and her own spear flashes at your throat") and ask, "What do you do?"

Make the PCs work for it. They might have to figure out a way to actually hurt this foe. They might need to Defy Danger to get close enough, or Aid each other to have any chance of overcoming its defenses. They might need to use the environment to their advantage. They might have to retreat or flee because they just can't hurt it. They might need to wait for their moment. They might need to do something drastic.

Reward creativity and effort. If they have an idea or a move that would work—even one you never expected—then run with it. Be a fan of the player characters. But also, respect your prep and the fiction. If your notes say that this monster is hurt only by bronze, and they don't have any bronze, don't let them steamroll you into agreeing that it's also vulnerable to, oh, silver.

They're exploring the ruins near Three Coven Lake. The room gets suddenly colder and the lanterns flicker, and (after a 6- to Seek Insight) a long, hand-like shadow reaches out and grabs Vahid. He drops his lantern and starts shaking in a fit. I address the others: "What do you do?"

Caradoc doesn't hesitate. "I draw my knife and slash into that shadowy limb, trying to cut Vahid free. Clash?"

"No, don't roll." I reveal an unwelcome truth. "Your knife goes right through the shadow, like there's nothing even there, but your hand goes numb and there's frost on the blade. Rhianna, Blodwen, you see this happen, what do you do?"

Blodwen looks at her possessions and says "Bendis root! I've got some from my herb garden." She drops her staff, sets down her lantern, and Has What She Needs to produce some.

"It'll take a few moments to get it out and light it. You still do that?" (tell the requirements and ask). Yup, she's doing it. "Rhianna, what are you doing?"

"This is like a ghost, right? So what hurts ghosts? Iron? Silver?"

That's Knowing Things, for sure, and she rolls a 10+. "Silver. In fact, you're pretty sure that's why Vahid got that silver dagger last summer."

"Oh. Oh! I'll step in and pull it off of him, then attack this thing."

"Cool, roll to Clash!"