I'm curious: What RPG worlds have you combined most successfully in a crossover setting as a GM? (Or what was the best crossover that you played as a player?)

My best experiences almost always included Chaosium's Call of Cthulhu or White Wolf's (old) World of Darkness (and their respective systems). The longest crossover campaigns we played were:

  • a CoC / oldWoD campaign, in which player vampires/werewolves investigated their own relationship to the Mythos which mostly replaced their own official origin stories. (We used the Storyteller system for this.)

  • a CoC / oldWoD / SLA Industries campaign, which was loosely related to the abovementioned one, and in which the players as SLA Operatives faced the Elder Gods and their oldWoD-based minions in their company-assigned quest to conquer "Earth". (We used a homebrew mix of SLA/CoC rules for this.)

What combinations would you recommend, what crossover is worth giving a try?

  • \$\begingroup\$ Since this became a Community Wiki, I'd like to see it reopened. \$\endgroup\$ – OpaCitiZen Jun 19 '12 at 7:16
  • \$\begingroup\$ This should not be reopened. Per our guidelines on sys-rec questions, Questions should be specific enough that there can be a single or best answer. This is just asking for people to relate their experiences. There is no objective reason to vote for one answer over another. \$\endgroup\$ – Pat Ludwig Jun 19 '12 at 15:24
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    \$\begingroup\$ Removed CW, as it is no longer appropriate. CW is a marker to be free to edit a post (as in answers that require heavy community involvement to stay current/comprehensive), not as a means to shelter questions that don't meet the guidelines or the faq. I recommend Role-playing Games Chat as a forum for this type of discussion. \$\endgroup\$ – AceCalhoon Jun 19 '12 at 16:03
  • \$\begingroup\$ For clarification and explanation (of guidelines) see this question on meta. \$\endgroup\$ – OpaCitiZen Jun 20 '12 at 6:43

10 Answers 10


I've played in a few PbEM's that were basically the old World of Darkness with a major Lovecraftian theme and they seem to be both popular and succesful. There was also some stuff put out by pinacle to bring oWoD werewolves into the Weird West (of Deadlands) that a GM friend of mine used somewhat sparingly to good effect.

... me personally, I have run a Firefly/Serenity game set in the wider Aliens (and Predator) movie universe. It worked pretty well as the majority of the themes and tropes are already in place (mega-corporations are the same as oppresive governments after all). Early sessions were just treating the firefly planets and political set-up as a small system on the edge of Colonial space and then we later moved up the scope so the players were interacting with a larger galaxy and some of the traditional 'company as bad guy' plots.

  • \$\begingroup\$ I ran an Aliens (world) / Cthulhu (world+system) crossover myself this last spring and it was fun - however, I really like the Serenity vs Predator idea, which, though quite close to what we played in feel, is in many respects a fundamentally different milieu. Although all the other answers have provided quite good ideas and suggestions, I'm accepting this answer as I think this is what I'm most likely to give a go in the near future. Thank you, and thank you everyone else for the great answers. \$\endgroup\$ – OpaCitiZen Oct 9 '10 at 6:59

I'm going to recommend GURPS, the Generic, Universal RolePlaying System, in case you've never run across it. GURPS is designed to handle any setting you can throw at it. The default setting for the current edition of GURPS is the Infinite Worlds settings found originally in GURPS Time Travel

The shortest distance between any two settings is GURPS.

That said, pretty much any setting-agnostic system should be good for doing crossovers. We used the PDQ system to handle our revisit to the Scion setting when we got so sick of Scion's native system that we just couldn't stand it any more.

You might like Savage Worlds, too.

A large part of this decision will come down to which system you like, how much weight you want, and how much work you need done for you. GURPS is heaviest of these that I recommend, yet it has the most support and the most work done for you, in terms of there being rules / stats for anything you can think of probably already available.

  • \$\begingroup\$ Thank you, GURPS might really worth re-checking. (The last time I checked it, ages ago, I was completely turned off by the illustrations - that's a drawback of being a graphic designer... But I digress, sorry. So, maybe the newer editions look more "appetizing".) Btw, I may have misconstrued my question, as what I'm primarily interested in is (your experience concerning) crossovers of truly different worlds and systems that were not designed to be combined and used together. \$\endgroup\$ – OpaCitiZen Oct 5 '10 at 18:15
  • \$\begingroup\$ Ah. I see. Well, I am glad that I have given you a useful answer to a different question! :) I will write another answer here that will, with any luck, be a good answer to this question! \$\endgroup\$ – gomad Oct 5 '10 at 18:24
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    \$\begingroup\$ On your other topic - the 4th Edition of GURPS received a total graphic overhaul. It is one of the best RPG series around for layout and clean, usable page design to my eye. And indexing, especially cross-volume indexing. However, I'm a writer and a systems geek, not an artist or designer, so I couldn't say with any certainty if you'll like the new look better or not. But I would say that many GURPS supplements are worth having on your shelf even if you don't play GURPS - you'll find few better RPG guides to people, tech, and animals! \$\endgroup\$ – gomad Oct 5 '10 at 18:42
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    \$\begingroup\$ If you're going to downvote, you might want to leave a comment telling me what's wrong with my answer. "I don't agree" is not the same as "This is a bad answer". How will anyone improve the answer if we don't know what caused the downvote? \$\endgroup\$ – gomad Mar 29 '11 at 16:27
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    \$\begingroup\$ off: @gomad: I do agree with that, downvoting should probably require an explanation (of course, coming to think of it, in the case of plain bad answers - which yours imo was not - that would be tiresome, so I'm not 100% on this.) @whoever downvoted gomad's answer, could you please explain your reasons for it? thx. \$\endgroup\$ – OpaCitiZen Mar 30 '11 at 12:40

There are several generic systems with multiple genre sourcebooks.

EABA has some fantasy, sci-fi, and post-apocalyptic setting books, and a system that can run from street-level supers down to kids in the hood... and mid-magic high fantasy as well as paranormal-free.

CORPS, by the same author/company as EABA, has fantasy, horror, and post-apocalyptic settings, as well... and was originally a moderns conspiracy game. It runs no paranormal to street level supers or low mana magic, fairly easily. It handles power levels in the same ranges as EABA.

Hero System can handle nobodies (-25 point incompetent normals) to demigods (5000 point greek demigods), and has genre books for SF, Fantasy, comic book supers on both street level and 4 color, as well as comic book magic-based supers, Chanbara and Realistic Martial Arts, moderns, Cyberpunk, horror and westerns. (Sups from 4E to 5E are perfectly useable with either edition; 6E has some differences.)

GURPS has more Genre books than any other game I know of. Many complain that it doesn't do genres as well as other games mechanically, adapting the setting to the engine, rather than the engine to the setting.

TORG is a genre-mashing game... Earth invaded by alternate realities. PC's from any one... and not of need the same ones. tech-free magic heavy to Cyberpunk, at least three kinds of horror, several action-adventure oriented cosms, 2 different cyberpunk realities... It's pretty wild. Currently not in print, may still be available electronically and some FLGSs have it still.

d6 system is likewise multiple systems with the same core rules distributed, and a variety of genres. Counting stuff that's hard to find: Superheroes, fantasy, Star Wars, MIB, Indianna Jones, non-SW space opera, horror ... easily cross integrated. Now open-licensed, too... hard to find in dead tree.

All of the above can readily genre-mash. I've mixed streetlevel supers with fantasy in Hero System; Fantasy with Illuminati University in GURPS; Humor and Fantasy in CORPS. EABA's settings include a few with some genre-mashing already. Torg is a blast... but if one doesn't like genre mashing, it is going to be unhappiness generation...

A few others I've not used, but know people who have.

Paladium Books' games Since they all use pretty much the same system, they can be used readily for mash-ups. System of questionable merit to many; fans tend to be quite vocally in favor of it.

Chaosium's BRP and derivatives... The various games all scale the same, so characters from one can be used in another easily. various rules in older editions don't match up, but can easily be ported. One bloke I know of used CoC's sanity rules in his ElfQuest game. Another used EQ for the elves in his non-EQ RuneQuest III game.

D20 3.0 SRD derivatives. Too many individual things to list; most stick close to core d20, and can be mixed and matched with only minor issues. Everything from Dune-meets-Warhammer-Feel (Fading Suns D20) to biblical fantasy, and most points between.

All of these have a variety of strengths and weaknesses; some do certain genres really well and others poorly (EG: GURPS Supers in mashups tended to have issues with mages being WAY more powerful at the 300-500 point range than supers...) that are too much to handle in this already long answer.

  • \$\begingroup\$ An excellent list, thank you - though I must admit what I've been looking for primarily is not a world-independent engine to run wild crossovers with but a combination of worlds and (their) systems not designed to run together. \$\endgroup\$ – OpaCitiZen Oct 5 '10 at 18:41
  • \$\begingroup\$ Fading Suns is a worthy mention. It's such an amazing setting because you can run just about any style of campaign you can imagine. Dungeon crawl? Gothic Horror? High Tech espionage? any of the above, and more, can easily work within the setting as established. \$\endgroup\$ – Stephen R Feb 5 '18 at 23:48

I'm having huge success with a crossover of Greyhawk and Earthdawn. I'm using the Earthdawn 3rd edition rules/setting and importing huge chunks of chewy gygaxian dungeon/hex-crawling. Extremely fun so far.

[A comment on the previous Earthdawn/Shadowrun conversation...

Earthdawn is recognized by the FASA designers as Shadowrun's mythic past (the peak and fall of the previous mana cycle).

"Atlantean" tech are references to the isle of Thera (modern day Santorini). There are characters who live through (some of) both settings, like Queen Alachia, and the Dragon Dunzelkahn/Mountainshadow.]

  • \$\begingroup\$ I guess you're using Earthdawn mechanics, Greyhawk setting and flavor. With Horrors? That sounds pretty cool... \$\endgroup\$ – Simon Withers Jan 27 '12 at 0:45

D20 Modern Urban Arcana and D&D 3.5 are explicitly written to allow for crossovers. The crossover is more commonly from D&D to D20 Modern than vice versa, but there are notes for doing it both ways.

Unfortunately both are out of print, but should be reasonably available.

  • \$\begingroup\$ This combination sounds fun as well, though I'd be more interested in crossovers involving games and systems not designed to work together. :) \$\endgroup\$ – OpaCitiZen Oct 5 '10 at 18:19
  • \$\begingroup\$ I recall D20M UA being released at the time of 3e rather than 3.5, are you sure it's 3.5 that it's explicitly written to allow for? \$\endgroup\$ – migo Mar 28 '11 at 19:41
  • \$\begingroup\$ @Migo might well be for 3e. \$\endgroup\$ – C. Ross Mar 28 '11 at 19:48

Shadowrun and Earthdawn. Although SR and ED are not mechanically compatible to each other the share the same metaplot of their background, although separated by over six thousand years.

There is also at least one (older) official published adventure involving SR and ED in a cross-over campaign (Harlequin's Back (spoiler!)).

  • \$\begingroup\$ This is a good one, and I must admit we did play such a campaign as well (and it was good, no doubt), yet I'd be more interested in crossovers of games/systems not designed as explicitly related to one another. :) \$\endgroup\$ – OpaCitiZen Oct 5 '10 at 18:21
  • \$\begingroup\$ I'd argue that SR and ED aren't designed to work together as they only loosely are related thematically, and have unrelated mechanics and subsystems. \$\endgroup\$ – migo Mar 28 '11 at 19:42
  • \$\begingroup\$ @migo: SR and ED are much more than "loosely related". Take a look at this short list - too much identical names too be pure coincidence in my book. Also, the mechanical differences of the systems are irrelevant to the answer (see the OP's comment) and even then the metaphysics of the two worlds are related closely enough to match. Further, both the SR and ED wikipedia entries mention the relation, alas without citations. \$\endgroup\$ – user660 Mar 28 '11 at 20:06
  • \$\begingroup\$ Barsaive doesn't have any Earth analogue, even though it's called Earthdawn. The setting is different. You've got Orks and Trolls in tons of other games as well - they're fantasy staples. ED and SR are as related as Rifts and RuneQuest. \$\endgroup\$ – migo Mar 28 '11 at 21:07
  • \$\begingroup\$ @migo: "[...] Indeed, the map of Barsaive and its neighboring regions established that most of the game takes place where the Ukraine and adjacent Russia are in our world. However, the topography other than coastlines and major rivers is quite different, and the only apparent reference to the real world besides the map may be the Blood Wood, known as "Wyrm Wood" before the Scourge and similar in location and extent to the Chernobyl (Ukrainian for "wormwood") Zone of alienation. [...]" Apparently the maps and wikipedia disagree with you. ;) \$\endgroup\$ – user660 Mar 28 '11 at 21:20

Any percentile system (BRP, Chameleon Eclectic, OpenQuest, FASA Star Trek etc) is fairly cross compatible, even with d20 roll under systems (AD&D, and in particular the complete Psionics Handbook. Because of the nature of percentile systems, converting characters is far more straight forward than any other type of system, which lends itself incredibly well to genre mashups.

Most ORE systems are fairly compatible, again due to the nature of the mechanic and how it tops out at 10d10 for the pool. Nemesis, Reign and Wild Talents are all fairly compatible with each other, and Monsters & Other Childish Things as well to a lesser degree (A Dirty World sits on the side entirely).

Dice pool systems like Shadowrun and World of Darkness are very compatible as well, the odds of 5 or 6 on d6 are roughly the same as 8, 9 or 0 on d10, so again any dice ratings can be easily converted one way or the other.

FATE based systems, particularly thanks to how Aspects work are also quite cross compatible, and Starblazer Adventures and Legends of Anglerre are even explicitly designed to support unusual genre crossovers.

Interestingly, the SAGA system used in Dragonlance 5th Age and Marvel Super Heroes is with only slight modifications compatible with the D6 system used in Star Wars. This is noteworthy because SAGA uses cards and Star Wars uses dice.

Not surprisingly, Aces & Eights and HackMaster Basic work fairly well together, given the latter was derived from the former.

A lot of games from when AD&D was at its most popular were pretty much clones, while changing the theme. Palladium Fantasy RPG was so close that I read a Palladium supplement without having read the core rules and understood every little bit. The BECMI and AD&D lines were also very close to being compatible, and there are a lot of other games which fit in quite easily, including BRP.

As for worlds, there are countless mashups that can work. The entire Urban Fantasy genre is a mashup in itself. Starblazer Adventures (the comics) as well as some supplements in Star Wars showed a solid combination between fantasy and sci-fi (the French comic series Ythaq also does this), and something like Sliders taken to the next step would do this as well. There have been X-Men and Star Trek crossovers, which worked quite well (in narrative). The Transhuman Space setting also begs to be mixed with something else, because by itself it's pretty tough to see what you would do, one idea I was particularly fond of was mixing it in with JAGS Wonderland.


I have run several crossovers (as I now understand the question!) that were not designed to be used together.

Most recently, I used the Company rules from Reign to supplement the disappointing (in my view) realm management rules from the latest A Song of Ice and Fire game. I think it worked reasonably well - my players did not like the change mid-game - but the ASoIaF rules were (again, in my opinion) a poor and nonsensical add-on to the game, whereas the Company rules in Reign are designed to generically handle groups - from a small group like a gang, through a guild, through an empire. I was able to use the realm management rules to do what I wanted - which was to both drive and reflect PC action. If I were to run another ASoIaF game, I would use the Reign rules from the outset.

Previously, I mashed-up The Riddle of Steel and Ars Magica to produce a homebrewed Riddle of Magic. The game was basically AM's skills and magic with TRoS's combat. It was a short game, but, I think it would be worth pursuing the fusion experiment further.

PS - I hope the RPGGeek links are OK - I like the way it collects systems and products.

  • \$\begingroup\$ Thank you, these games seem well worth looking into indeed. (On the other hand, what I really was looking for is a surprising combination of systems and worlds. I do realize it was most likely my "bad" not wording the question precisely enough - it was my first question ever here, I'll try and do better next time. Voted up your answer, though, for it drew my attention to a few rather interesting options.) Thanks again for taking the time to answer twice! :) \$\endgroup\$ – OpaCitiZen Oct 9 '10 at 6:54

Labyrinth Lord and Mutant Future, being based on the same ruleset, are suitable for doing crossovers. (Just as early D&D editions and Gamma World—of which LL and MF are more-or-less clones—were suited to crossing over.) Possibly involving time-travel, or perhaps an adventure à la "Expedition to the Barrier Peaks" where you have Mutant Future squamous things somehow transported to your medieval D&D setting.

Although, if your LL game is gonzo enough, that wouldn't necessarily count as a crossover.

  • \$\begingroup\$ There will soon be a Starships & Spacemen version on the same engine, too, allowing trek crossover. \$\endgroup\$ – aramis Oct 4 '10 at 21:21
  • \$\begingroup\$ This sounds rather interesting - I must admit I've never heard of these games before, so I'll have to take a look at (some reviews) of them. Thanks! \$\endgroup\$ – OpaCitiZen Oct 5 '10 at 18:24
  • \$\begingroup\$ If it wasn't clear in the answer, LL and MF are (respectively) a clone of Basic D&D and a game inspired-by-but-not-a-clone-of Gamma World. There's a nice overview of these and other retro-clones right here on RPG.StackExchange. Both can be downloaded as free PDFs if you are intrigued by the reviews you dig up. (I suggest RPGnet as a good place to start.) \$\endgroup\$ – SevenSidedDie Oct 5 '10 at 22:14

Old World of Darkness (and possibly new as well) and In Nomine work so well together at times that it's painful. (And so poorly at others that it's even moreso. The mechanics conversion is a fright, but the settings mashup in a variety of interesting ways.


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