I treat Defy Danger exactly like the Act Under Fire move in Apocalypse World.

Whenever a character does something that obviously demands a roll, but you don’t quite see how to deal with it, double check first whether it counts as doing something under fire. Come here first.

On a 7–9, when it comes to the worse outcome, hard bargain, or ugly choice, you’ll need to look at the circumstances and find something fun. It should be easy to find something; if there weren’t things to go wrong, nobody’d be rolling dice.

That last emphasis is mine. If there really and truly is no danger or consequence being risked, then you probably don't need to require a move at all.

You could absolutely use a single Defy Danger move to resolve the entire chase if that's what you want to do. It totally works, as the danger being defied in that case is 'the Orcs get away'. If that's too "zoomed out for you" you could break the chases into several smaller legs, each requiring a separate Defy Danger move. There's no right answer here other than which one you prefer. It's worth pointing out though, that each Defy Danger move you require for the chase needs to have some sort of consequence. It could be as nebulous as 'the Orcs are farther down the hallway' as Nifelhein suggests, or it could be something like 'you need to drop item X to keep up'.

I think this has been discussed elsewhere (or maybe I heard it in an interview), but none of the moves in Monsterhearts really solve anything. They don't resolve problems, only delay them or just end up making them worse. That's kind of the point, as the game is all about petty teenage drama. Only the Growing Up moves end that cycle.

So yeah, the Vampire's Cold as Ice seems like it'd cause more problems. But that's arguably the point. :)

This isn't specific to Dungeon World, but can apply to starting any game especially one shots. Just start the characters in a situation where they know what they are supposed to do.

To give you an example, here are the three set ups I've used so far.

• After exploring the local temple and discovering it was really a front for the horrible Snake Cult, you're hot on the trail of some cultists and the poor villagers they've kidnapped. They're not bothering to hide their trail, are about a day ahead of you as far as you can tell, and are headed right into the Rushmoor swamp.
• You've been following the strange tracks through the Wildwood for two days now. The trail leads directly from the village of Nordmark through the forest and out onto the ice shelf, heading in the direction of Whitespire Tower. Rumor in the village is that the Ice Witch has somehow taken up residence there again.
• As you follow the passageway down, it suddenly opens into a long rectangular room about 20' wide and 50' deep. Two rows of humanoid statues with upraised swords form a sort of aisle down the center of the room, the last two flanking a door. The Annulus, a legendary magical helmet, must lie somewhere further into the tomb of the Faceless One.

From there I start in with the questions to determine fiction. I ask loaded questions that will give me something to work with regardless of what the response is. Who sent you to go retrieve the Annulus and what does it do? How long ago was the Ice Witch defeated and what happened to the knights sworn to prevent her return? How  did the villagers not know the high preist was actually a Snake Cultist? Etc., etc., etc. Build on the answers by asking other players for details or clarification.

Yes, this is railroady. You're forcing the players to follow the Snake Cultists, to go explore Whitespire Tower and deal with the Ice Witch, or to search the Faceless One's tomb for the Annulus. But I think most players appreciate a clear direction and a clear goal for the adventure right from the beginning of the game. Especially for the first session. Drop the characters in the middle of a situation where the players can say "Ah ha! That's where I'm supposed to go" and just go.

noclue neatly summed up what I was trying to articulate before; that leaving the decision of who wins up to the fiction doesn't automatically mean that the PCs will win. You're supposed to "Play to find out what happens" and to "Fill the characters' lives with adventure". Additionally, as the GM you're allowed to "disclaim decision-making" as stated in the Apocalypse World book.

Also, I don't think that anyone is saying to ignore previously established fiction, AmPm. If it's already been established that one side is indeed faster/slower than the other then, unless something changes in the fiction, in my opinion it makes perfect sense for that side to win/lose. No one's saying to suddenly make the Fighter's chain hauberk heavier than it's been before, or to have the Orcs magically sprout wing on their feet and be as fast as the Flash. Sometimes you just have to make up stuff on the spot that hasn't been established yet. Has the Fighter been in a footrace while wearing chainmail before? If not than I don't see it being a problem to have them Defy Danger with either STR or CON to keep up. Again, this all circles back to the "Fill the characters' lives with adventure" agenda. If the action being taken doesn't have any possible chance of danger either a) you aren't looking hard enough, or b) the action isn't worth making a move over.

All that being said, if it's been established that the PCs and the Orcs are both relatively the same speed and the Orcs have a huge lead down a perfectly featureless hallway, I don't see the PCs having much of a chance to catch up.

I've done a single chase scene while running DW so far, but it was the reverse of your situation, SarahNewton; the characters were trying to get away from a pack of Winter Wolves. There were on only one or two Defy Danger moves resulting in misses, and the characters got surrounded. Oops. Although your situation is different, I don't really think you need to create a custom move (although I too love making them), as Defy Danger already covers everything your Stop the NPC move does.

Basing the custom move on the Aid/Interfere move works too, but unless the character has a Bond with the entity they're chasing, the player will always just roll+0. That's not a bad thing, it just seems harsh to me (like the Last Breath move). Also, as NPCs never roll dice, you have to find another way to give them the bonus or penalty that might result from the move. Monsterhearts does this well with it's Advantage/Disadvantage mechanics.

I'd also respectfully disagree with AmPm and samuraiko a bit. The players shouldn't know that they will catch the Orcs simply because you're leaving it to the fiction. If the fiction dictates that the PCs will catch the Orcs with little to no trouble, then why have the chase scene at all? If, for example, the GM has described the Orcs as being heavily wounded or otherwise slowed down, then the GM could just narrate the characters catching up with the Orcs and go from there. The chase isn't important. What is important is what happens next. If you really wanted to make a move, Defy Danger could be used to see how well the Orcs prepare themselves (if at all) before the PCs get within striking range.

Conversely, if the Orcs have been described as being excellent trackers and woodsmen or being in territory they know well, then they'll probably get away from the PCs if left to the fiction. That's where another Defy Danger move can be used as the characters attempt to find shortcuts, predict where the Orcs are headed, or just try to put on an extra burst of speed. My point is, you don't know who is going to win the chase, unless you've established that one side or the other has a commanding advantage. Play to find out what happens, remember?

Also, as Archangel3d said, chases are rarely just a simple race. There's all kinds of dangers and problems to deal with. noofy is dead on with the suggestion to "zoom". You could resolve a week long chase with a single Defy Danger move, or you could zoom way in and have characters make moves for each  "comic book frame". What dictates the "scope" of the action is player enjoyment. Sometimes we want to see each and every little thing that happens, other times we want to get right to the resolution.

If you are going to base the adventure on the unleashed demons and the portal, start with the witch already bein dead, they are standing over her corpse as the laughter of her demonic pact-holder rings around them. That makes the front simply the demon prince and his hordes.

That was definitely something I considered, Timon. The game would have been very different if I'd started them over the corpse of the Ice Witch and went from there.

Instead, I started them about two days journey from the spire (to have them make an Undertake A Perilous Journey move) and asked a bunch of questions to establish how the Ice Witch escaped her prison, how long before the village was completely deserted, why the villagers were unable to protect themselves, etc. I figured that they'd get to the tower fairly quickly and dispatch the Witch. Little did I know that they'd:

• meet a friendly Ice Elf patrol who'd escort them to a secret tunnel to the spire's lower levels;
• be ambushed by a pack of Winter Wolves;
• make it to the secret tunnel just before the wolves, due to the sacrifice of their elven companions;
• fight a demonic yeti, and make camp in it's lair to recover;
• encounter one of the 13 cursed knights who had broken their vows and released the Ice Witch;
• discover the knights wanted to be released from their curse;
• and have the knight lead them right to the spot where the Ice Witch was completing her ritual.

In other words, nothing went as I expected it to but that only made it all the more awesome! The session ended with the Dwarven Cleric bull-rushing the Ice Witch into the demonic portal she was conjuring. The player got a weak hit on his Defy Danger move, so of course the choice I gave him was a) knock the witch partially through, merely delaying her for a bit, or b) get her all the way through by hanging onto her and going through himself. The player chose option b, and the screen faded to black with the Elven Bard composing a ballad for his heroic companion while settling in to wait for his (hopeful) return. Awesome sauce.

Luckily I have plans to expand the adventure into a "campaign starter" with a few more dangers, and so had a vague idea of what steps the Ice Witch would take as she was ramping up to the final summoning. Those turned into quick and dirty Grim Portents during the adventure, which gave me a few moves to make (mostly Show Signs of an Approaching Threat) on player misses.

I also ran another game (with a different setup) that didn't have a Front or a Danger. I won't say that game was a failure, as there were a lot of other factors to consider (more players, reactive instead of proactive monsters, pure dungeon crawl, etc.) but comparing the two, things go a lot smoother when you have a Front and a Danger to work with. Lesson learned. Make Fronts. Even for one-shot games. Also, Dangers that can't further their own agenda are boring. Don't bother with them.

Dude. mease19. That's even better. Screw starting the session with the PCs heading into to kill the Ice Witch. They've already done that. Now they're at the bottom of the tower (it's sunk deep into the ice from a past age) with the Ice Witch dead at their feet and they have to get up and out.

Of course without her controlling magic holding them in check anymore, the ice demons she'd summoned are going ape shit...

This isn't uber-creative or anything, but there were two missed Discern Realities moves in the game I ran a few weeks ago.

The first one was when a character listened at a door (which, upon retrospect, didn't require him to make the move at all). I told him that he heard gently lapping water, as if there was a large body of water on the other side. Which there was; the "room" on the other side was a 30' diameter underground lake with an Otyugh lurking in it.

There really wasn't anything else going on in the location the characters were in, I had already used previous misses to set up stuff in other locations (thinking offscreen), and I couldn't think of a move that fit the consequences of the action (which is why I probably shouldn't have required the move at all). So I just "banked" my GM move for use later. I then used it to deal damage with the Otyugh when the characters turned their back on the open door. Or rather I tried to. There was a mix up in player/GM communication and it turns out the characters had closed the door before they turned. I turned it into a Defy Danger move to get the door shut before some tentacles came through.

The second one was when someone went to explore a dead end hallway. It was getting towards the end of the session, and so I decided to go nasty; I put a Green Slime on the ceiling to put them in a spot. I guess the move wasn't that hard, as I gave the character a Defy Danger move to get out of the way before it dropped on him. I suppose I could've just dealt damage as it reached out and engulfed him with it's pseudopods, but that seemed unfair.