"I don't like this," said Michael. "If you ask me, it's too risky."
"Says the guy who always takes point," said David.
"That's because the party makes me do it! 'Send the rogue in,' they say!"
"Or because you want to snag some loot before the rest of us see it!" said Samantha. "I've seen your Sleight of Hand modifier, mister!"
"Still, Melantha agrees with Mikko," said Ally. "We have this misty silver archway and these strange twisted metallic things all over the place here. This place ain't right."
"Wimp!" said David. "We came here to find the greatest mithral strike ever, and we've already found some. We're about to find the mother lode. We'll be rich and famous, and Rashean Bantecou is all about both."
"But where did the mithral come from?" asked Michael. "Look, Mikko is a dwarf. He knows mining, and it's obvious they didn't dig it up here."
"Hey, Melantha," Samantha said. "Don't forget it was your divination spell that said, 'The high silver sails on the silver mist and through the mists shall you find the boundless source."
"Yeah, like that's not vague enough to ride a mastodon through," Ally said. "I've got a bad feeling about this."
"Well, no time like the present! I shall hie me hence to the boundless source of high silver! Rashean Bantecou AWAAAAAAYYYY!"
With that, Rashean leapt through the mists. The others followed, finding themselves standing amidst the twisted wreckage of some sort of strange metallic framework towers, once unimaginably tall but now in shambles. The only signs of life were criss-crossing bootprints and slithering tracks, seeming to lead toward a great mound in the distance.
"Well, guys," said David, "I don't think we're in Kansas anymore. "
WORDS TO THE WISE
Why are the PCs there? What is the point of world-hopping? Mostly for variety, but it should usually be a time-limited go-and-come-back mission. Be very careful with allowing permanent world-to-world access.
How do they get there and get back? Are they zapped off by an angry archmage and have to find their own way home? Do they control access between worlds? Is someone back home going to retrieve them after a certain amount of time?
How will rules change? How do D&D skills (especially Craft, Knowledge, Profession, and Speak Language) change in the new world, if at all? Does magic (whether arcane or divine) operate differently? How do people from each world view those from the other, especially different races? How much rules conversion is needed to make D&D characters fit with the new world (and vice versa)?
What about the stuff? Do items from one world work in the other? Temporarily or permanently? Can they be replicated (or repaired) by non-natives?
How different is the new world? Are you just skipping from one D&D campaign setting to another (Forgotten Realms, Greyhawk, Birthright, Mystara, Dragonlance), to a different D&D genre (Oriental Adventures, Ravenloft, Al-Qadim, Dark Sun, Planescape, Spelljammer), another d20 system (Star Wars, Wheel of Time,d20 Modern), or another system and/or setting entirely?
Where are they? Presumably the party has gone through a gate of some sort. Eddie, being the devious DM that he is, might make the whole "gate" (and what lies beyond) an elaborate illusion! But let's say it's real. What happens now? For Mikko, Arphaxad, Rashean, and Melantha, the first order of business is to find out where they are. They could be anywhere, anywhen, from elsewhere in the same dungeon to another world entirely, or maybe another plane like the metallic cubes of Acheron. Only the DM knows for sure. . . .
As it turns out, the characters have eloped beyond the realms of D&D into another game world. Eddie, bless his nostalgic soul, has fond memories of his days playing games like Gamma World, Traveler, and Star Frontiers (and AD&D adventures like Expedition to the Barrier Peaks, Tale of the Comet, and even "City Beyond the Gate" in Dragon #100). He thought it might be great fun to drop the party from his D&D campaign into a whole new postapocalyptic sci-fi world!
If you feel similarly inspired to attempt world-crossing with your gaming group, there are different ways to go about it but they all take some work. You could create an adventure with the flavor of postapocalyptic sci-fi, maybe using oddball D&D monsters that have a creepy/alien/mutant feel to them. If you want to get ambitious, you could convert monsters, items, or adventures from other games into D&D stats. For some things, conversion might be easier using the d20 Modern rules, which are better set up for technological items. The rules for D&D and d20 Modern are not exactly the same, but close enough that they can work together. If you get lucky, you might find game statistics that have already been converted by someone else, whether that means a fan website with a few favorites or a full-scale, professionally published d20 system conversion (like Star Wars).
Eddie had some time and decided to do it himself, using d20 Modern as a guide. He had a lot of fun going through the old books and cooked up an adventure arc for the PCs involving one of their old adversaries, who discovered the gate before them. The villain made deals with the evil spacefaring worms on the far side of the gate, setting up an intergalactic trade of zombie slaves and mind-control magic for priceless metals and technological terror! Eddie dropped in a little radiation hazard, some deranged mutants, a little trip into space, and of course a classic wands-versus-blasters shootout!
Sound interesting? Eddie has built up enough trust with his players for them to cut him some slack if he brings up an oddball idea. They also like sci-fi games on occasion, so the diversion is not going off in a direction no one but Eddie is apt to enjoy. He knows his players, and so should you, including the limits of their tolerance. Ally, Samantha, David, and Michael aren't going to be too happy if the campaign shifts permanently to the spaceways -- after all, they are playing D&D and not a sci-fi game for a reason! -- but for the duration of a story arc, they can go with the flow.
The most important questions to answer are: How do the PCs get to the new world? Why are they there? And how do they get back? Eddie has laid the bait and set up the adventure, setting the stage for the party to explore the new world and learn some of its strange mysteries before eventually discovering their D&D-world enemy plotting with the alien mutant menace. Once that happens, the party can bust up the conspiracy and seal the gateway to this freak-infested universe to forestall any future alien invasions. The mission has a clear and attainable end-goal, though PCs should still have the opportunity to "sightsee" a bit before they return home.
The mechanics of cross-genre gaming are important, because they can have a big effect on how much fun a player has. If all of a sudden the characters' deities are hard or impossible to reach, Melantha is going to be pretty hosed and Ally not very happy. Likewise, if technological traps and such are impossibly tough for a D&D rogue to do anything with, or if the party gets to fight only robot constructs immune to crits (and sneak attacks), Mikko is going to suffer a major reduction in effectiveness and Michael is going to howl loud and long. Even communication is a major issue: Can the party talk to the people in the new world? How will NPCs from the new world react to alien/foreign PCs?
In combat, are the party's weapons, armor, and spells going to be effective in the new world? It's okay if they work a little differently here (for example, some enemies might have DR/energy weapons, high-tech weapons might bypass some or all of a character's armor bonus, technological items could require Exotic Weapon Proficiency for PCs), but be wary of massively handicapping characters or imposing a style that is radically unsuited to the characters in your PC party.
Once you open the doorway between worlds, you also have to decide what happens to stuff brought from one side to another. Do technological gadgets still function in a magical world, and vice versa? Is it just a matter of limited (and presumably nonreplaceable) charges? Can technological items be replicated with magic (or vice versa)? Say Mikko gets killed (again) over in the alien world; could Michael bring in a new mutant or alien character?
Maybe the biggest question of all is whether to let PCs go back and forth between worlds more than once. Usually it's best to answer no, even making destruction of the gateway a necessary part of the adventure. Things can get out of hand if you have a clever player like Samantha dreaming of all the ways she can manipulate the gateway for fun and profit, and limits on cross-world items may prove moot if it's possible to go through the gateway to resupply. It might work, but consider carefully the long-term campaign impact if the worlds are permanently joined and decide whether that's how you want the world to evolve.
Although Eddie is doing a sci-fi crossover, the same principles apply when going to any new plane of existence or even other D&D campaign settings, whether an alternate "standard" (pseudo-medieval Europe-ish) D&D world like Krynn (Dragonlance) or a more exotic setting like Rokugan (Oriental Adventures), Zakhara (Al-Qadim), or Athas (Dark Sun). It's more complicated when you go beyond the borders of D&D, whether into other fantasy like Wheel of Time or sci-fi like Star Wars or anything else you can imagine. But if you have the time and the inclination, a cross-world adventure can be a lot of fun. Maybe your PCs will team up with some Marvel superheroes, like mine did many years ago, and have a darned good time doing it!
About the Author
Jason Nelson lives in Seattle with his wife Judy, his daughter, Meshia, his son, Allen, and his dog, Bear. He is a full-time homemaker, part-time Ph.D. candidate in social & cultural foundations of education, and is active and committed born-again Christian. He began playing D&D in 1981 and currently runs one campaign while playing in another.