How can I combine very different role-playing systems with D&D 5e?

Question

I'm planning on making a D&D 5e campaign for my friends so they can experience what an okay DM is like rather than a bias and railroading DM which is so far their only experience of Dungeons and Dragons. In the campaign I'm creating, There is going to be magical artifacts that distort reality, time, and space. One of the ways I want to do this is for reality to shatter/merge with other realities to make it so different RPGs have melded with their world. These are the RPGs that I either have a solid understanding of or an okay understanding of:

• Honey Heist
• Call of Cthulhu
• AD&D 1e
• Monster of the Week
• Rifts
• Twilight 2000

I really like the idea and I want it to work but I have a lot of flaws and complications in my plan:

1. Almost every one of these RPGs has a different game system and has different game mechanics.

2. The list of RPGs that I know have varying levels of complexity, and I'm afraid that going from Honey Heist to Twilight 2000 is going to give a player whiplash.

3. Calculating what your rolls are can be extremely confusing if you don't have a good grasp of the game and these fusions of RPG systems are going to be the same length of a one-shot which is not enough time to fully grasp the rules.

4. Weapons and armor and all of that would be confusing to transition to some games like Call of Cthulhu where fighting back isn't that much of an option, well it is but it'd be a TPK. But in D&D 5e, class revolves around the way your character fights and what do you add to help the party not die in the encounter. This is also an issue for Honey Heist where it'll be hard to skills if someone gets the Hacker role and the closest thing to technology in their world is some oil lanterns and a bunch of healing potions.

I have many ways to implement these games into 5e like

• Making only the NPCs use different gaming systems
• Creating a homebrew gaming system so they can easily go from RPG to RPG
• Have them continue to use the d20 system no matter the game
• Scrap the idea
• Let them use the other RPG character classes like subclasses and tone down their abilities a tad
• have only small portions of the other games be included like just the and that's it.

Here's my problem:
How do I include these different RPGs into 5e, and how do I do it in a way that is simplest for the players and myself?

Answer 1

This is hard work and probably a bad idea

This is not the answer you want to hear, I suspect, because you've offered a bounty for it. But, this is mostly a bad idea, for all the reasons you listed above dealing with mechanics.

RPG mechanics systems are tools-- they're designed to achieve certain effects and to support certain game worlds, and almost none of them are designed to be compatible with any other ones. Heck, even most of those game worlds are not compatible with the other ones: What obvious, or even plausible, translation exists between a D&D cleric and the Twilight 2000 game world?

Then realize that you have to do that at least six times (for your six desired games) and you have to do it faithfully enough that all the various characters and support gear from each system translates correctly.

There is no 'simplest,' here, this is an inherently complex task.

But if you absolutely must....

...Then at least use a tool designed for it. Do not fixate on translating everything into 5e. This is emphatically not what 5e was designed to do. At all.

There are a few RPGs that are at least deigned to emulate multiple genres, usually referred to as "generic" RPG systems. As it turns out, I have some limited experience in going to and from these generic systems. If you must do this, translate everything into that one chosen generic system and run with it.

One is GURPS, where I contributed an answer along these lines. This, at least, is sorta what GURPS is meant to do, although in my direct experience, it won't do it very well, and you will still need to do a lot of heavy lifting to convert all those systems. But it will be better than trying to use 5e.

There are other possibilities and I'm certainly not going to list them all, not least because I don't have experience with them all. I will list one more, though, for a particular purpose: Everway was not designed with genericity in mind, but it does seem particularly well suited to it. (I include that link not because it has details on how to adapt Everway, but only to demonstrate that I'm not the only person who thinks this.)

I have experience playing in an off-genre Everway game, and it works very well for what we want it to do-- well enough that in my copious free time, I am also adapting it for a Star Wars game.

The real reason I bring up Everway, though, is to drop one more observation and contrast on you: Some generic games (like GURPS) are detailed and rules heavy. Some (like Everway) are very rules light and abstract. If you go this route, I strongly encourage you to go toward the rules-light end of the spectrum. In my experience, it just works better because there's a lot less work to do.

---

Now, I realize that what I've just said is, "Don't do this. This won't work, and if it does it won't work well. If you really must do this, do this substantially different thing instead."

But that's the best honest advice that I can provide with well over three decades of gaming experience.

Answer 2

Don't Do It

I'm planning on making a D&D 5e campaign for my friends so they can experience what an okay DM is like

If this is your goal, then keep the game simple. Attempting to add all those disparate elements is going to create confusion. Show them the game straight and clean, earn their trust and help them understand it. Don't run outlandish high concept games when you're dealing with skittish¹ players.

In the campaign I'm creating, There is going to be magical artifacts that distort reality, time, and space.

This sounds like a recipe for disaster. Unless the players have direct control over it, messing with the fundamental nature of the character's universe is going to feel exactly like the railroading you're trying to avoid.

¹_{Not really the word I want, but the right term escapes me.}

Answer 3

Run one-shots.

I would heavily advise against trying to blend game mechanics from two different systems together, aside maybe from AD&D which at least shares a rough power parallel. You can't run Monster of the Week enemies in D&D because Monster of the Week enemies don't have actions and do whatever you want. You can't run Honey Heist enemies because there aren't really combatants in Honey Heist outside of a general idea of obstacles. The games are "speaking different languages" to the extent that they don't share common concepts, and you're not likely to easily find ways to put content in D&D that it doesn't know what it is.

So run one-shots. A lot of gaming groups will take one-session breaks from one system to play another.

(Breaking for a one-shot at the session break will also let you consider how to adapt the current circumstances to the reality shift that just happened.)

The Reality Shift That Just Happened

You can, however, at least attempt to recontextualize the story of one game in the story of another. You can track down a reality escapee with Monster of the Week or steal a delicious, sticky reality heart in Honey Heist.

Your D&D weapons and armor can still kind of carry over, but more as story objects with whatever rules track reasonable ones that already exist, because reality shift. The new game rules can largely apply in a D&D flavored setting, because reality shift. A tiny red panda with a VR headset plugs a cable into a rectangular opening in a magic circle and says "I'm in." Why not?

Try to bring back what people liked.

At the end of your oneshots, there's a practice I often see in my playgroups called "roses and thorns" or "stars and wishes" depending on how positive you're feeling - ask people to tell you something they liked about the system and something they wished they would have seen. If it's possible, you can bring those play concepts, if not the precise play mechanics, back into D&D. Or maybe there'll be something in the story they liked, which is easier to transfer.

Answer 4

Virtual Reality

Make it so the "real world" is the D&D campaign. The players need to save people trapped inside various magical artifacts. These artifacts present a wild, but satisfying reality to the occupants trapped within, and they won't even think of trying to escape without outside influence. The only way the party can free them is to enter the fake reality created by the artifacts, find the people and convince them to free themselves.

Upon entering each artifact, they make a new character appropriate to the game/setting. You might consider giving them some kind of bonus based on their D&D character. You might also let them learn how to cheat (ala Neo in The Matrix) in specific ways after they've gotten used to travelling to the "dream worlds" or "pocket universes" embodied by the artifacts.

If you do go this route, I'd suggest having the first adventure be short (1-3 sessions maybe?) and use as similar of an RPG as possible (AD&D maybe!). Also don't make "VR death" lethal in "reality"... Maybe if they die inside one of the artifacts they're just kicked out, and can re-enter it after a long rest. Or maybe they take Psychic damage. If you feel the need you could even have Stat or Max-HP damage as a consequence... but I'd only recommend doing this if they're treating it too much like a video game and getting themselves killed frivolously.

Finally, after the first "vr session", check in with the players Out of Character and make sure the players are cool with it. If they like it, there's a lot you could do: they might want to revisit previous "dream worlds" to learn spells or find magic items. Maybe there's multiple people trapped in the worlds that the players most enjoyed playing (or you enjoyed running. If they're on the fence about it, you could still employ this but keep each "vr session" to a single session mission so they're still mostly playing D&D with the occasional "one shot" of something else while still maintaining some narrative continuity.

Answer 5

(I'm assuming you will have the Cleric cast their spells in T2K - if not, this advice might be WAY off) Take each game's base rulebook. Somewhere in there it will give a range for attributes & difficulties (i.e., Average is 11 out of 3-18 or 4 out of 1-6 & Easy is 10 on d20 or 3 on d6). Draw a sliding scale from lowest to highest and place the values for Minimum, Average & Maximum, then place others as needed. You should soon see that 5 on 1-6 = ~14-15 on 3-18 (& so on). Grab what you need for the PCs, some NPCs & your coming adventures and do the conversion for the next session (or 1-2 sessions per environment if the Players can determine the next reality).

Not quite what you are doing, but I once wanted to create a very violent modern horror game. I removed the cyberware from of Shadowrun v2 (left in vehicles, weapons & non-decking computer rules - but just called them modern versions of themselves). I took Werewolf: Apocalypse, Vampire: Masquerade, Call of Cthulhu & Chill and converted just the items, actions, spells, monsters and contests I wanted to use with this method, and added a couple attributes (e.g., Sanity). I found the players were very forgiving of where I eyeballed it wrong, instead being thankful for the new experience.

Answer 6

Do you have the source books to the other systems?

My suggestion would be, if you do have the books, in your session zero have your players role up characters for 5e, this seems to be the base system you would like to run as your main. After that have them role "alter-ego" characters for the other systems. This wouldn't have to be entire characters but only those things which would make those characters cross over into the other systems as painlessly as possible. Make these sheets addendum's to the main character sheets. As you move through your adventure you could have some kind of plane-shift take place and their "alter-ego" takes over.

Something like in movies where the real life person gets sucked down the rabbit hole and is now a cartoon. They are the same person but now all the rules to play by are completely different. Anvils can fall on their heads but that doesn't mean they die but rather have to be flat for then next few seconds while everyone laughs at them. It is meant to be a little confusing and disorienting. They will have to feel their way through and figure out what being in this new surrounding means and what the consequences are. In the end I think you may have a great adventure on your hands. It will be a little complicated at first but in the end could be a wild ride your players talk about for years to come.

Have fun!

Answer 7

If you can get your hands on the D20 version of Call of Cthulhu, I suppose you could stretch the rules to cover both fantasy and modern/horror "worlds". Where "modern" would include Twilight 2000. RIFTS is probably way beyond that, and I am not familiar with Honey Heist (I googled and I see it, too, is "modern", but you would probably need to add feats/ad-hoc skills to cover the genre).

Answer 8

My suggestion would be keeping the 5e system as a base and adapt everything else to that system using just elements, characters, etc., but not their mechanics.

You could also add some special event that mechanically works as a mini-game of sorts using a different system borrowed from any of the others RPGs.

As an example, my first 100% homebrew campaign's BBG was a Blood Elf. As there was no such race, I took inspiration from WoW's board game (which, to be fair, uses the D&D 3e system) and adapted it to 5e.

I also ran a mini-game where the players had to solve a puzzle and use actual spinners to prevent a temple from falling down over them.

My point is that 5e is a system that can make virtually anything work. If you are running a 5e campaign as you said, add as many elements as you want but don't change the core system or it will stop being a 5e campaign.

Hope this helps and, ultimately, be sure to keep it entertaining for your players and have fun, that's the point of all this.