Using Spout Lore to reveal a detailed, pre-created world is contrary to the rules.
There is a caveat I should make here. I'm going to talk about rules the GM has to follow. You're welcome to not consider them binding rules, but DW as designed does. If you don't follow the GM rules, you're "voiding the warranty" on the game and it will not operate as advertised. You're on your own then. (Incidentally, this is a close paraphrase of the designers [on p. 159 and in various conversations] – it's not just me saying so.)
For reference, these are the GM's responsibilities:
- Describe the situation
- Follow the rules
- Make moves
- Exploit your prep
… plus following the Agenda and Principles.
So part of your job is to "exploit" your prep, as in mining it and twisting it for the benefit of the current game session. You also have to follow the rules, which includes your agenda. And your agenda is (p. 161):
Your agenda makes up the things you aim to do at all times while GMing a game of Dungeon World:
- Portray a fantastic world
- Fill the characters’ lives with adventure
- Play to find out what happens
Note that doesn't say create a fantastic world – "portray" is a very deliberate word choice, as we can see by continuing the same quote (emphasis mine)…
Everything you say and do at the table (and away from the table, too) exists to accomplish these three goals and no others. Things that aren’t on this list aren’t your goals. You’re not trying to beat the players or test their ability to solve complex traps. You’re not here to give the players a chance to explore your finely crafted setting. You’re not trying to kill the players (though monsters might be). You’re most certainly not here to tell everyone a planned-out story.
So that's the trouble you're having: Spout Lore does let you, the GM, reveal a detail, but Dungeon World itself doesn't permit you to have revealing a big pile of pre-crafted details to be part of your agenda. Spout Lore isn't a opportunity to infodump on your players. In fact, it encourages the opposite with the agenda "Play to find out what happens." That includes about your world.
So why does Spout Lore not work well with pre-crafted worlds? Because in many subtle ways, the answers that players get won't be as interesting to them. The setting detail revealed existed before the PC did, so it's only maybe relevant or interesting to them and their adventures. (Note that Spout Lore requires the GM to say something interesting about the subject.) You are quite understandably going to be way more excited by pre-created setting details you reveal than the players are. If the Spouted information isn't as interesting as it could be, their motivation to use the move decreases. If it decreases below a certain threshold, they'll start seeing it as a "dead" move – one not worth taking when the risk is getting a miss. Other moves become much better value propositions for the same amount of risk.
Something created on the spot or quickly adapted to current circumstances and the flow of the game will be much more relevant and interesting to the players and their characters. By holding your world lightly in your mind and being willing to kill your darlings, you are serving the GM's agenda better. You're serving your players better, too. You can more easily come up with details that are pertinent, and more easily adapt the loose details you do have in your prep to your players' current game input, and as a result come up with something that's way better because it's leveraging the collaborative-narrative design of Dungeon World.
The answer to your specific question is that due to the result of 8, which falls into the category 7–9, the villain gets to make an attack. That does not automatically mean that damage will be dealt. The GM has the choice to use one of the NPCs monster moves, which can be anything from simply doing damage or throwing a net at the PC to calling support. This entirely depends on the monster in question, and how the GM might have set up the monster with individual touch. Usually the monster moves are something that makes sense for that type of monster.
From the rulebook (page 56):
The enemy’s counterattack can be any GM move made directly with that
creature. A goblin might just attack you back, or they might jam a
poisoned needle into your veins.
In your specific situation, if the GM chooses to deal damage with the monster, the damage die of the monster is rolled and the PC is damage accordingly. However, damage is only something very abstract. If in the fiction the enemy does not simply deal some damage, but more like cleaves a bloody gash in your leg, this should additionally be taken into account in the fiction - like, it will be difficult for the PC to cling something or run fast until the wound is treatet.
However, I suspect that you want more than the answer to your specific question.
The general answer to the question "How does combat in Dungeon World work?" is that combat is a dynamic string of actions in the fiction that drive the overall scene back and forth. The players describe their actions, and according to the fiction moves are triggered. One of these moves is Hack & Slash. Depending on the results of the roll, everything might be fine (10+), there might be minor complications (7–9) or there might be major complications (6−). Depending on these, the GM has the chance to react to the players' actions with GM moves. These are specific moves unique to the GM that exist to drive the action forward. On a 7–9, as already established, the GM may use a monster move of the monster that was involved in the initial roll. On a 6−, the GM has the option to make a soft or hard move from the list of GM moves. These include the monster moves like above, but also environmental moves, such as dungeon and world moves, and a number of generic moves like use up their resources or separate them. Depending whether the GM chose to use a soft or a hard move, the consequences will be narrated in the fiction and then the players get a chance to react again, at which point the cycle starts again.
Best Answer
Know why it's not useful.
There are a couple of ways to approach the problem of presenting the PCs with information that is interesting, and not useful, and that is up to them to make useful.
They all start with coming up with something interesting, and it doesn't sound like that's a problem for you.
If the interesting thing is useful, come up with an obstacle to its usefulness that the PCs will have to navigate.
If the interesting thing is not useful, come up with a way the PCs can make it useful right now, or a scenario where it might be useful to the PCs, and keep that in your back pocket for when you need to prompt a PC to do something.
Barriers to Usefulness
So let's start with some useful information:
How can you make this not immediately useful?
You could introduce something else people would have to find out:
You could introduce a cost to pay:
Or an obstacle to overcome:
On a 6- you might consider severely ramping up one of these costs if you think it would go hard enough:
Pathways to Usefulness
Or suppose you come up with something interesting that doesn't look immediately useful. It's still got to present some hook - it's your play in the back-and-forth narration, so you should be setting the players up somehow.
Well, unless you're running a white-knuckle first session, the PCs don't have exactly one problem. And you knew the problem they were Spouting Lore about in the first place, right? Otherwise you'd have no idea what to say to be useful.
So look at all the other problems out there - all the fronts, and all the things PCs have cared about. If you can make it fit as a stepping stone on one of those, all well and good.
If not? Well, if you feel like it won't dilute things too much to open up another front or another ongoing project, go for it.