I love mashups. Whether in music, film, or elsewhere, a good mashup takes the best parts of its two (or more) constituent works and makes them even better by putting them in a different context. Mashups work just as well in RPGs. Shadowrun, a mashup of fantasy and cyberpunk, has been drawing players in for 35 years. Rifts, arguably an attempt to mash up everything the designer could think of, has created many more fond memories than its ruleset would suggest. For today, though, I’m going to dig into a more literal mashup, a setting where two worlds collide: an RPGnet thought experiment and proto-setting called The Long Stair.

As recorded in a long thread started over fifteen years ago, The Long Stair was intended to be a combination of ‘spec ops dungeon crawls’, Cold War shenanigans, and a little sprinkling of cosmic horror as D&D creatures made it ‘up the stair’ into the real world. While it’s certainly not the only way to do it, this setting illustrates a very well realized example of worldbuilding from a thought experiment, in this case the idea of sending modern-day operatives into a D&D dungeon.

The version I envision, with a working title of Forbidden Stairs, has a few other twists. One other clear inspiration is Rome, Sweet Rome, a short story by military historian James Erwin that gained some renown when he posted it in installments on Reddit. The story is one of a modern US Marine Expeditionary Unit that gets somehow teleported back to the Roman era. Erwin discusses the shift from the Marines’ superior firepower to their complete lack of logistical support, making for a nuanced and engaging story. When you combine the original campaign idea with the thought experiment of a military unit (extremely) far away from home, the overall conceit of Forbidden Stairs begins to take shape.

When the fissure is opened under a nuclear test site, it’s not a strange multidimensional dungeon on the other side, but a stone circle in a forest. Of course, after a few initial scouting missions, it becomes clear that the world on the other side is one of magic and monsters and horrors…but also one of elves and wizards, castles and kingdoms, potions and artifacts. Clearly more investigation will be needed. How did you find yourself signed up for a mission like this? Well, there’s no turning back now.

Forbidden Stairs takes a few liberties with the original premise of The Long Stair, but the most significant one is likely the mechanics. While the original premise is couched in the mechanics and genre assumptions of D&D, Forbidden Stairs is run using the parallel mechanics of two games from Free League Publishing: Twilight:2000 and Forbidden Lands. Thanks to the strong parallelism of these two Year Zero Engine titles, mixing mechanics for fantasy adventure and military survival is simple. And, thanks to how the rulesets work and feel, the strong contrast between modern military and medieval magic is maintained.

Premise

While there has been a lot of flavor and detail developed through the original brainstorms and forum threads, the basic premise of The Long Stair is relatively simple. At some point during the Cold War, whether by nuclear test or other unexplained mechanism, a fissure is opened in reality which connects our world to the world of Dungeons and Dragons, approximately. Realizing the great power potential of both the monsters on the other side as well as magic in general, the US government seals off the fissure with a massive vault and constructs The Long Stair, a set of forward operating bases designed to help stage missions into the other world. These missions are intended to collect powerful magical artifacts and (if the mission lead is foolish enough) live creatures to help bolster the American war effort. Of course, the Soviet Union catches wind of the whole thing and, before you know it, Cold War cat and mouse continues into a fantasy world.

One of the great things about The Long Stair is that, beyond being a very clever mashup, it offers potential for many different styles of campaign. While military expeditions into a fantasy realm are the obvious example (and the reason I picked Twilight:2000 as a system for conversion), the plotline supports spy games, conspiracy shenanigans, and even supernatural horror as creatures pass through the vault into the ‘real world’. There is both a lot of potential depth in this setting as well as a lot of potential for satire, trope savvy sendup, and plain old over-the-top shenanigans.

The reason Twilight:2000 works so well as a start point for the campaign is because it is basically a funhouse mirror version of fantasy game Forbidden Lands. Although the two games don’t match up exactly, they match up well enough that the necessary conversions fit, well, in a Cannibal Halfling article. They also provide enough grit in the simulation to provide some of the visceral thrill of mowing through trolls with automatic weapon fire that, let’s face it, D&D really can’t come close to. On the other hand, Twilight:2000 is more of a military RPG than many, and some of the campaign ideas less focused on ‘field operations’ may be better suited to a different game. That all said, if we start with the assumption that our campaign will focus around traveling from the real world to the fantasy world (and maybe back if you survive), Twilight:2000 is an excellent choice.

Mechanics

The main mechanical lift here is matching up Forbidden Lands with Twilight:2000. These mechanical guidelines are intended to minimize the amount of work necessary, and to place that work when it is needed on the GM. Players will create characters using the Twilight:2000 character creation rules, with no modifications needed to any part of character creation. They should be able to pick items out of the Twilight:2000 rulebook as normal, with changes only being necessary as they progress into the fantasy world.

When it comes to running this game, you should mostly be able to run things in parallel and not worry too much about conversions. Leave NPCs and monsters from the fantasy world with a Forbidden Lands stat block, and should the need for NPC skill tests come up, just roll them according to the ratings in Forbidden Lands. The only times that you’ll need to make changes are for combat and a potential stronghold.

You’ll probably notice that, on an average dice basis, Twilight:2000 characters are somewhat more competent than Forbidden Lands characters. While some of this is a statistical difference between the two dice mechanics, the primary reason Forbidden Lands characters skew to a slightly lower rate of success comes down to gear dice. In Forbidden Lands, gear dice provide additional bonuses to relevant tasks; in Twilight:2000, difficulties assume having the appropriate gear (though there are still a few bonuses to be found). For combat, this does mean we’ll need to retool the weapon and armor ratings to get the systems to align. For melee weapons, find the T2K damage rating by adding the damage and bonus together. You can find the crit rating by consulting the bonus. If the bonus is +1, the crit rating is one higher than the damage rating. If the bonus is +2, the crit rating is equal to the damage rating. As examples, this translates a knife (damage 1, +1 gear bonus) into the exact stats used in Twilight:2000 (damage 2, crit 3), and translates a scimitar (damage 2, +1 gear bonus) into the same damage stats as a machete (damage 3, crit 4). Give all bladed weapons an armor rating of +1, all blunt weapons an armor rating of +2, and all improvized weapons an armor rating of +3.

Ranged weapons are going to be a little bit different, especially given how they compare to firearms. Damage ratings for both Forbidden Lands and Twilight:2000 are the same; all ranged weapons have crit ratings one higher than their damage rating. Most ranged weapons are armor +1 except for crossbows, which are armor 0.

Armor will have to be reduced from Forbidden Lands to equate to the ratings in Twilight:2000; the armor rating reduces damage across the board to armored targets, which both scales better and also better simulates the armor-piercing abilities of firearms and explosives. Divide the armor rating of all armor and creatures in Forbidden Lands by 4, but round up. This means that plate mail goes from 8 to 2, making it equivalent to a plate carrier (although full-body). If anything this is generous; most tests have shown that plate mail gets perforated by modern rifle rounds. All footnotes for the armor still apply; plate mail modifies Mobility for T2K characters, and chainmail is halved (from rating 2 to rating 1) against arrows and stabs.

When looking at monster stat blocks, do take into consideration the Strength stat; given the Forbidden Lands stat block this is a proxy for both hit points and size. Luckily the bestiary entries list dice quantities for most attacks, so Strength can be treated fairly strictly as an HP pool. That said, as large Strength values also represent inhuman size or durability, we should adjust the attack rules to account for this. For every ten points of Strength, all attacks effectively have a Crit rating that is one higher than listed. That means that if a character were shooting at a small dragon with an M16, the weapon would have an effective Crit rating of 6. If you make a Called Shot this Crit penalty is reduced by 1; if you make a Called Shot after making a successful Otherworldly Lore check (see below for this), the Crit penalty is reduced by 2.

Instead of mucking around with additional skills, I’ve opted to add a couple of specialties to existing skills and keep changes to a minimum. Otherworldly Lore is a specialty for Recon. It both allows the character to try and find monster weak spots as above, as well as function much like the History specialty, except pertaining to fantasy situations which the character has otherwise never encountered. Similarly, there is an Arcanist specialty for Tech, which functions much like the Scientist specialty except for magical phenomena.

The last bit of rules adaptation concerns the home base mechanics. Home base construction in Twilight:2000 assumes enough bombed-out buildings and other wreckage around that construction materials aren’t an issue. Forbidden Lands, on the other hand, has much more robust rules around raw materials. This does tend to make strongholds much more expensive, but that’s the downside of existing in a functional economy! Below I’ve added raw materials requirements to all of the Twilight:2000 base facilities, using an analog from Forbidden Lands whenever one existed. The existing prerequisites all still hold, so make sure you can trek back to the modern world to get spare parts before starting on that garage. On the flip side, all of the stronghold facilities from Forbidden Lands (save those which are redundant) are also fair game; you never know how badly you need an iron mine until you don’t have one.

Base Facility	Existing Prereqs	New Prereqs
Cow Pen	Basic Tools, Cow	20 Wood
Cropland	Basic Tools, Plot of Land	None
Defenses	Basic Tools	600 Stone
Heater	Basic Tools, Fuel (firewood or alcohol)	20 Stone or 20 Iron
Infirmary	Basic Tools, alcohol fuel	100 Wood
Garage	Basic Tools, 50 general spare parts	200 Stone
Lookout Point	Basic Tools	200 Wood, 400 Stone, or 100 Iron
Pigsty	Basic Tools, Pigs	50 Wood
Prison Cells	Basic Tools	50 Stone, 20 Iron
Root Cellar	Basic Tools	200 Stone
Shrine	Basic Tools	80 Wood or 80 Stone
Well	Basic Tools	50 Stone
Windmill	Basic Tools, 40 general spare parts, 40 electronic spare parts	20 Iron
Workshop	Basic Tools, 50 general spare parts	200 Stone

Considerations

When looking into the original version of The Long Stair as a campaign setting, there is an implication that the environ on the other side of the fissure (portal, gate, etc) is a megadungeon. This does make for an interesting premise, but for the purposes of Forbidden Stairs, our version, I’m going to pull back from that. This campaign is best suited for a fantasy world that would fit well in a Forbidden Lands campaign, one with an expansive and dangerous overworld, fragmented political power, and powerful ancient ruins complete with artifacts ripe for the taking. If this sounds like many D&D campaigns, that’s absolutely a good comparison too. What we don’t necessarily want to do, though, is limit the setting to strictly a dungeon where many of the best systems within Forbidden Lands aren’t as applicable.

Another reason why Twilight:2000 is a great pick for this premise is that supply lines are an incredibly important element in whatever missions your party will take on. In the fantasy world, there’s no ammo to scavenge, no spare parts to find, and as far as your high-tech gear is concerned, no backup. This means that your party will have to plan carefully when it comes to resources like ammo. If for some reason the vault were to shut behind them and trap them in the fantasy world, they might do well to consider ditching their firepower for some local armaments.

While you can be as hard or as easy on your players as you want, I think this campaign will sing when the contrast between worlds is emphasized. In the fantasy world, make ammo count, food and encumbrance a constant struggle, much like in the apocalyptic setting of Twilight:2000. On the other side, though, you can stop tracking everything, it’s fine to go fire off a hundred rounds down at the shooting range, and sustenance is only a hallway and a hamburger away. The other contrast to emphasize is magic. One suggestion I have is that if you want to use magic artifacts as written in Forbidden Lands, keep the artifact dice. Adding a third d8 or d10 to certain rolls is huge in Twilight:2000, and luckily the mechanic should keep its wow factor even with the different dice basis.

This also means that it’s more than okay to lean into the power fantasy, though if your players want trouble, let them have it. Some of the bigger monsters in the Forbidden Lands bestiary would obliterate starting characters…and it turns out if those characters have automatic weapons, they might still get obliterated. That’s part of the fun of a scenario like this, and you can have some truly memorable encounters if you let the power level creep up to match the firepower level.

Where I think this premise begins to have some real long-running potential is when you start considering the impact on the fantasy world as a result of these incursions. Updating the stronghold rules is an important part of setting the groundwork for having characters (player character or otherwise) who are operating in the fantasy world long term. Maybe the party has to go extract a Colonel Kurtz type who has set up in the fantasy world. Maybe the local king has put a bounty on the head of ‘the otherworld invaders’. Hell, maybe it’s a goal of one of the characters to learn magic. What then? The possibilities are vast, and amplified by having essentially two worlds smushed together which you can draw from.

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Forbidden Stairs is not only a reinterpretation of the themes of The Long Stair, it’s also intended to be a campaign which, provided you own copies of Twilight:2000 and Forbidden Lands, you can go set up right now. Want to give Forbidden Stairs a try? Do it! I’d love to know how it goes. Have you run or played in a campaign inspired by the original Long Stair concept and discussion thread? I’d love to hear about that too. Genre mashups like The Long Stair have existed pretty much as long as RPGs (technically longer in other media), but as the games we have at our fingertips keep getting better and more expansive, there are more and more things just waiting for us to try. Hopefully that’s given a few of you some thoughts about how you’d explore Forbidden Stairs.

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