Classic Megaman (AKA Rockman) games maintained a nonlinear structure: they presented the player with a stage select screen showing the set of bosses they could fight, and allowed them to choose which one they wished to pursue. Death in a stage sent them back to the selection screen, allowing them to give up on a frustrating level and try something else if they wished. The clever part was that each boss granted a special weapon when defeated, and each boss was typically weak to one or more weapons obtained in other stages. This meant that, through trial and error (or strategy guide), one could work out an optimal order in which to beat the bosses: picking a relatively easy one at first, then a second boss that was weak to the weapon granted by the first, and so on. Once all eight normal stages were cleared, it unlocked the final set of stages, which usually included rematches with all the prior bosses, allowing the player to demonstrate their memory of which attack modes made shortest work of which bosses.
Despite the many lessons learned from other games, I’ve virtually never seen an analogous progression structure in a tabletop RPG. Arguably Yazeba’s Bed and Breakfast is a contender here since you begin with access to several scenarios that can be replayed and unlock further scenarios, but it’s in service of very different goals, lacking an exploratory adversarial element. The nearest practical equivalent is an open world-style hex (or point) crawl – there are multiple sites of interest and you can return to them with tools acquired from others if you wish – but the friction of traveling between adventure sites is so great that one rarely exhibits the same behaviors.
It’s an interesting system, though, one that rewards the kind of problem-solving deliberation TTRPG people love. It’s not overly difficult to implement, either, especially if one melds in the concept of gating progression behind acquisition of key items found in Metroid, Castlevania, and Legend of Zelda games. Therefore, I’m going to tentatively dub it the Key Item Campaign Structure.
KICS
The bones of the concept are simple. First, establish a “home base” of some kind that the players return to after every adventure. Next, lay out several adventure sites they can travel to from their base: the classic number is eight. Finally, create a separate adventure site that can only be reached after handling the others, to act as a climax to the campaign. Once this last site is cleared, the campaign concludes.
A baked-in assumption here is that the campaign has a definite beginning and ending, with the spine of a single overarching goal. Open-ended forever campaigns are all well and good, but people have busy lives and it’s nice to actually reach a narratively satisfying conclusion to a campaign within a reasonable amount of time. The idea here is that you establish the stakes of a Problem in the first session, spend several sessions attacking sub-sections of the Problem, and then use that momentum to fully solve the Problem – or die trying, or watch the world burn, of course. Ideally each adventure should be tightly designed enough that it can be finished in a single session, to decrease the time between meaningful decisions of where to go next. There’s a lot to be said here for setting up a primary antagonist and framing each sub-adventure around one of their subordinates, in the style of Dr. Wily and his Robot Masters: it’s easy to grasp and puts a face to the threat in a way that evokes an emotional response from players.
The details of how you implement this structure depends on the setting you’re using it for. Since I’m embedding it into Protoplastic, I’ll refer to that to show how the parts fit together, but the possible variations are considerable.
Home Base
This can be a hub city, a tramp freighter, a gang hideout, or anything else you can reliably assume the PCs will loop out from and back to each adventure. If possible this should be more or less centrally located on the campaign map, or otherwise justified in its equal ease of travel to the other sites, such as by teleporter or itself being physically mobile. While not strictly necessary, it’s a great opportunity to include a base building mechanic, letting you upgrade it with resources gathered during adventures to augment your team’s abilities in the future: better equipment, researching for more details on what an adventure site will include, and so on. Travel to the sites themselves should be relatively de-emphasized, perhaps the equivalent of an interpersonally-focused camp scene or a single travel event roll, if not elided entirely through hard framing questions.
In Protoplastic the base is the home island of the heroes, and it also serves as a kind of session 0: the first session is the backstory of the lives the PCs lived before their journey, and includes the adversary (the main antagonist played by the GM) interacting with them to establish a relationship and clear threat from the start.
Adventure Sites
Although the classic number of sites is eight, it’s probably the upper limit to present at once time without overloading the players with information. You could go as low as three if you wanted, and six (as in the first Megaman game) would be a pretty reasonable number. However, you can bypass this issue by splitting the sites into groups: starting in Megaman 7, some games would only let you choose between four stages, and unlock a second set of four once you’d cleared them all. There’s a lot to be said for this model, especially if you’re playing a game with character advancement that dictates harder challenges over time. To manage this, make access to a second set of sites somehow diegetically contingent on completing the earlier ones. For example, if the second set are all deep underwater, the PCs will need to acquire a submarine “liberated” from an enemy stronghold in the first set – or if the second set is in a forbidden land beyond a great wall, completion of the first set might convince the king to authorize the party’s travel beyond the wall. This is the Metroidvania-esque part of the system, similar to requiring a double jump or magic key to reach certain parts of a dungeon.
This same method of separating adventure sites allows you to block entry to the final zone until the players have completed the others: even if you acquired a submarine to reach the second adventure set, you might need an airship to reach the castle in the sky where the dark lord dwells. If you like, you don’t strictly have to gate it off, though: you could allow the players access to the last location right from the beginning, but simply make them too powerful to feasibly face at that point. Instead, each other zone they claim increases their power and reduces the main antagonist’s, until they judge their relative strength favorable enough to attempt a final attack.
In Protoplastic, each adventure site is an island menaced by a particular monster or villain. You start out with three islands to sail to from your home island, “unlock” the second set of three by acquiring a new part for your ship that lets you bypass a barrier trait the islands in that set possess, and finally unlock the stronghold island of your adversary with a second ship part that negates the barrier trait of that island.
Information
For this entire premise to come together, it’s important for the GM to liberally hand out information about what will be in each adventure site. At minimum, the players should be made aware of what each location is, what the antagonistic force is, and what method it’s using: “A desert town suffering night raids by undead bandits” would be reasonable, as would “A space station plagued by biomechanical aliens abducting people”. Arguably you could give even more information than that, framing it in terms of traveler’s rumors, intelligence reports, or prophetic visions. In Megaman you gain that information through failed attempts at beating a stage, but a TTRPG doesn’t have the luxury of spending that much time, so it’s better to just give that information freely. You want to establish enough details that the players can formulate some sort of basic plan: they know, perhaps, that a red dragon is there, so they prepare ranged weapons and fire resistance spells.
Upgrades
The remaining piece of the puzzle here is the upgrades the player characters receive, the equivalent of the special weapons that deal extra damage to certain bosses. In an RPG context, the most obvious ones are simply that, elemental weapons: if you know there’s a fire boss and an ice boss, you can make the decision to fight the fire boss first, then use the flamethrower you get from it to first-turn melt the ice boss. It also includes pretty much anything that would be traditionally seen as a “magic item”: phasing cloaks, darkness lamps, and so on, all useful when operated cleverly. In Protoplastic, such upgrades are the entire progression system: you are made out of plastic parts, and so is everything else, so when you defeat a creature you can slot its parts into yourself to gain its power. You don’t necessarily have to go that far, though: even just treating it like a more intentionally placed version of a standard D&D-style magic item economy still fulfills the role as long as the artifacts are designed to interact with the other adventures in the campaign.
That’s what this is, in sum: a way of writing adventures in view of the campaign as a whole rather than purely self-contained to the adventure itself. Each session of your campaign can be an exciting new challenge, yet predicated on past challenges and looking forward to future ones, all drawn into the gravity well of the final boss. A campaign can be a skeletal structure that supports the adventures within, rather than simply a big sack containing them.
