The original idea is to create a “megadungeon” of some sort for Dungeon World, to capitalize on it's current popularity. This has expanded into becoming an entirely new game that is essentially a hack of Dungeon World, so we could include entirely new mechanics and such to support the concept. Generally we want more to leverage off DW's extant mechanics to get what we want, before we go replacing any of them.
Will the game be completely stand alone, including it's own list of classes and monsters and such that might be redundant with DWs, or is it an “Expansion” to DW that simply adds rules, new monsters, new classes, etc. Making it an expansion has the advantage that it would get the support of the original DW designers. Otherwise we might steal some of their business. Would also make the game smaller, and probably more marketable, too.
The first genre proposed was some sort of crawl through an “underdark” type area, to support some sort of “surface” community in trouble. Charles has proposed that we reinforce this thematically by making there only be one city on the “surface,” but to have that city be in a tiny ball at the center of the world, with the sun (or something like it) at the absolute center, ala Pellucidar.
Do we want to do the Pellucidar thing?
Centralizing Concept = that part of the premise of play that keeps the characters from spinning off in all different directions.
Optimally the game will be created so that mechanically it can be inserted into another ongoing DW game. But it may work best to have chargen be specifically for the game, so that specialized rules can come into play that will create a centralizing concept and/or hooks that have to do with exploring the underworld area in question. Otherwise the challenge is to both leverage off what currently exists and make the new rules such that they can be incorporated into a normal game of DW. The extant rule that currently feeds into this is bonds… Players just have to tailor the bonds in question to have involvement with the adventure in question.
Hopefully whatever centralizing concept we come up with, it's better than the typical versions ((“the king asked you to,” “Everybody else is busy with a war on the surface, and only you can be spared,” “you are criminals who have been sentenced to death, who will be pardoned if they do this,” etc, etc, etc). Bonds do this somewhat, but basically we can suggest bonds that create the specific concept. For instance if it was folks sentenced to death, bonds would be like “__ committed his crime with me, and I'm angry that it was his fault we got caught.”
Possibly leaving more complex versions of these as a scope for more detailed Faction game supplements (incorporating a full set in this concept would likely just dilute the focus), one idea to create character involvement in the underworld is to have them create bonds with the community, or have moves with them to get community support, etc. The notion being to find some creative ways to give incentive for players getting interested in the sort of exploration we're looking to see happen in play. And to entangle them in potentially interesting faction conflicts that could lead to PC conflicts as well.
This is just one idea of how to create such a link into the action. There may well be other, better ways to proceed.
A classic of early dungeons, we can expand on the concept of “rumors” by creating the NPCs behind them, and developing them into full-fledged “quests.” So instead of hearing of a famous gigantic gem, the person telling the PCs about it wants them to get it. Those telling false rumors may have specific agendas for doing so (some may just be misconceptions and the like, though). Unlike most pre-published scenarios, however, these quests and rumors should work into PC issues so that it becomes personal, and not just a run for money.
Do we want to make the game solely stand alone in terms of chargen to focus on creating proper characters? Clever GMs and players will figure out how to convert in any case. Perhaps we can include conversion notes or methods?
What other creative centralizing concepts can we come up with?
Each run down should present lots of branching choices, each a whole adventure itself. The choices themselves should be interesting plot elements, in terms of prioritization. Grimm Portents, Doomsday clocks, or similar mechanics can be used to convey this sort of thing. Do I choose this impending doom, or this other impending problem?
The place should not just be fantastical, but fantastical even by the standards of the adventurer's lives. The underworld is a metaphor for leaving the known realm of light, and going into the unknown. Literally going under should be a trip into an “otherworld” for the PCs, which makes even the departure and return parts of the trip uncertain. Perhaps even finding the entrance is difficult. Entering should mean getting past guardians. The game should have a mystical quality to it, and we can focus better on the mystical and magical rules to get there.
Keep touchstones that are memetic, but don't steal or mimic specific stuff. So we'll have dwarves, and dwarven cities underground, but not specifically mind-flayers, or even flind-mayers. We can invent stuff as interesting or better.
Unlike your standard dungeon, where at best you have perilous journeys to get to the dungeon itself, the vast underground realms themselves will involve many perilous journeys, often with the loss of rations or whatever, and many specific dangers along the way. Keeping track of resources becomes a real challenge, not being able to easily backtrack to town all the time.
In addition to just hiking through the caves of the underworld there should be opportunities to take boat-rides, Tram cars across chasms, even flying through giant chasms on the backs of some sort of tamed beasts. There may be magical gates that link up places, or which lead to otherworlds (plan an Otherworld supplement?)