1. Obstacles are anything interesting that will prevent the PCs from accomplishing their Objective.
Obstacles can be anything – monsters, enemy agents, traps, hostile terrain, puzzles, walls, unendurable weather, curses, diseases, disguises, bureaucracy, organizational schisms. Anything that could prevent the PCs from accomplishing their task, and which you believe will be fun and interesting for them to contend with.
2. Each game suggests particular kinds of Obstacles.
The genre of game will suggest certain kinds of Obstacles. In Dungeons & Dragons, you expect terrifying monsters, evil wizards, and fiendish traps. In In Nomine, you expect angels and demons operating as covert agents – both agents from the other side, and rivals within your own side. Mouse Guard, you expect inclement weather and wild animals.
Nothing stops you from going outside these suggestions, but you’ll want to think hard for a few moments before you do so. Here’s why: the Obstacles are a huge part of what sets one game’s adventures apart from another’s.
You can absolutely pit your D&D party against social taboos and bureaucratic entanglements, and have your In Nomine group delve into ancient crypts and slay monsters. And some groups will love that! But some groups will complain that “This doesn’t feel like D&D.” And they’ll have a point.
I’m not saying don’t do it, but consider that angle, and your particular players’ expectations of the game, before you do so.
3. Obstacles can be tied to the Objective, to the PCs, or to the road between them.
PCs tend to run into Obstacles for one of three reasons.
Sometimes the Obstacle has it in for them, and them in particular. Maybe they have prices on their heads, or some particular NPC wants revenge on them. Maybe the villain knows they’re coming, and has sent agents to hunt them down before they can become a problem. Whatever it is, it sticks to the PCs. It’s after the PCs. They are the reason it’s in play.
Sometimes the Obstacle is intimately tied to the Objective. The treasure is surrounded by traps and puzzles, at the bottom of a dungeon full of monsters. The villain lives in a sprawling castle, full of bodyguards and magical defenses. The Holy Grail looks like any other cup. These are all Obstacles that are innately tied to the Objective itself. They stick to the Objective; they’re often created by the Objective. They’re not tied to the PCs, or particularly aimed at them; they’re just there to meet all comers.
Sometimes the Obstacle is just along the way. The Fire Swamp in The Princess Bride and the Space Slug in The Empire Strikes Back are both good examples of Obstacles that are just along the way. They’re not tied to the PCs or to their Objective; they just happen to be near the road the PCs take. I recommend caution when including Obstacles of this kind – it’s very easy for the PCs to just miss them altogether. You’ll need to make them flexible, so they can be used even if the PCs choose an unexpected mode of transport, or call on an unexpected resource.
4. Obstacles should be mobile, or cover all paths.
All right, I’ve been itching to tell this story, and I think this is the place for it.
In a Pathfinder campaign I ran years ago, the PCs were students at a magic school in Absalom, the huge city at the center of the known world. I had an NPC who was a school chum of theirs come to them for help. He’d effectively dropped out several months back, but hadn’t bothered informing the school or his parents of this fact, and had been living on the money his parents sent him for school. He’d just gotten word that the school was finally going to terminate his enrollment – and send a letter to his parents to this effect. He wanted the PCs to stop the letter from reaching his parents.
So, I figured the two likeliest options for the PCs were (1) intercept the courier carrying the message, or (2) break into the school’s admin office, and modify or destroy their friend’s records, to prevent the letter from being sent. For the former, I statted a courier, and gave her some interesting magical defenses, and I picked a few vermin for the PCs to encounter while chasing her through the streets. For the latter, I found a nice office map to use for the school administration building, and threw in some security measures and potential witnesses.
The PCs chose (3) trick their friend into murdering his own parents, then “resurrected” them for him by hiring a couple of doppelgangers to impersonate them, so the PCs could take advantage of the parents’ wealth.
Yes, this party turned out to be pretty evil, and we can have a conversation about the implications of such a roleplaying decision, but my point is: these Obstacles were each tied to only one path, and couldn’t really be moved to a different path – and so when the PCs picked a path I hadn’t thought of, I was left with nothing to impede them. And from an adventure-flow perspective, that turned out to be fine. They set their own new objective from there – don’t get caught – with its own implicit Obstacles.
Traps guarding the treasure chamber, and fortifications around the villain’s home, are Obstacles that do a pretty good job of covering all paths. I mean, the PCs will find ways to circumvent them – that’s what PCs do – but that’s fine. I call that “solving” them, and consider it a successful outcome for the adventure. The PCs won’t accidentally pick a path that just renders them irrelevant.
Roving monsters, hired assassins, guardian constructs, the villain’s bodyguards, and of course the villain themself, are all very mobile Obstacles. With mobile Obstacles, you can move them around in response to PCs’ decisions. Again, the PCs will find ways to overcome them – that’s good; that’s the point – but they won’t casually render these Obstacles irrelevant with their choice of plans.
5. Three Obstacles seems to work well.
I find prepping three Obstacles – rather than two or four – works best for me. It tends to give me adventures that are of the right size.
I make them all different – some mobile and some covering all paths; some tied to the PCs and some tied to the Objective; etc. In an ideal world, all of your Obstacles would be mobile enough or universal enough that they would apply no matter what the PCs do. In practice, not every Obstacle you concoct will fit every situation, so you want some variety so that that unexpected left turn is unlikely to invalidate all of your Obstacles.
6. It’s common to quietly add or remove Obstacles on the fly.
Of all the elements in an adventure, the Obstacles are the ones I’m most likely to modify on the fly. Sometimes a section of your adventure will turn out to be unexpectedly flat, so you’ll want to throw in a guardian monster or magical barrier or natural disaster. Sometimes you’ll decide no, no, we’ve had like five combat sessions in a row; maybe I’ll hold off on dropping that other monster on them.
Tomorrow, the most nebulous element: Supplementary Information!