Wednesday, March 16, 2016

To what extent do you convert rules?

When you convert another game's setting, adventures, crunchy bits (equipment, monsters, etc.), or game elements (sanity checks, etc.), do you:

- convert them with maximum fidelity to the source rules?

- convert them with maximum fidelity to the end system's game rules?

- just pick something from the end system's game rules that fills the same need?

- convert in some middle ground kind of way?

For example, we're playing Gamma Terra. Gamma World has a random level up bonus chart, so our GM made up a GURPS-compatible version of it. When I ran GURPS 3e based Gamma World years back (my "Mutants & Mayhem" game), I didn't convert that - you just earned points like you normally do in GURPS.

For weapons, we've already seen some very Gamma World-like weapons, like Torc grenades. In my game, I just ignored most of the Gamma World weaponry and instead picked similar devices from GURPS Ultra Tech and handed them out. Where GURPS lacked something I felt was necessary, I just put it in and found something similar to nick the stats off of.

Rules like mutation, radiation, etc. I ignored and used GURPS rules instead.

I've done similar things in other places. I've converted a fair amount of D&D monsters to GURPS in my day. Back in my first games, I often directly ported effects over. 50% Magic Resistance? Roll percentile dice, see if the spell works. These days, I'm more likely to say "Magic Resistance works like in GURPS." My old, old sheets said stuff like "+1 Puissance or silver to injure." These days, more like Accessibility-limited Damage Reduction. When I did a pirates game that was based on a game and setting that had primary, secondary, and tertiary characters, I just did 100, 75, and 50 point characters. And of course when I ran AD&D, "converting" D&D monsters was as simple as just not using the Morale stat and adding "evil" to the end of Chaotic on most alignments.

I'm curious what other people do - I'm sure for most it's a mix. But what do you favor? Pull the mechanics for, say, Sanity right out of Call of Cthulhu and use it bolted on to your system? Change it to something that fits the resolution in your home system? Ignore it and make up a new rule entirely? Pick one that's close enough?

Conversion is a funny thing - what you demand out of them can be very different from another GM. And what you get by the decisions you make can change the flavor of your game immensely.


  1. I tend to play low fidelity GURPS (few optional rules in use outside of tactical combat) but if I'm using non-GURPS material I tend to convert to low fidelity GURPS-style 3d6 based rules. NPCs are often *very* low fidelity.

    For example, sectoids in my WWII/X-COM/War of the Worlds mash-up had a psi attack, but I didn't dig deeply into GURPS psi rules - it was just a quick contest of skill vs will with range modifiers and three possible effects (win, win by 5+, win by 10+ or crit). Similarly they had mediocre weapon skills with a psi-HUD that used servos to aim their neem guns at the point they wanted to hit. It was in rules terms some sort of accelerated time rate only for aiming or equipment equivalent thereof, but I just added a reasonable neem gun acc to their base skill and said they never aimed.

    In neither case did I care about the fine details of GURPS rules or points, just what to roll 3d6 against and what the effect was.

    1. I don't think that's low fidelity to GURPS, otherwise even my current DF game is showing low GURPS fidelity. That's just low detail.

  2. For GURPS Gamma World, I'm taking some original GW material, modeling it in GURPS using my own rules, some good, some admittedly kludgy, and bolting it on. The best example is radiation. Using the GURPS rules for radiation (even the new ones in After the End) would be underwhelming in a game where radiation was meant to injure you, mutate you without injuring you, or simply kill you. That's more than a little silly, but it's Gamma World in a nutshell, and I feel a GURPS Gamma World game would lose out if its radiation didn't yield similar results.

    Other rules are close enough that GURPS rules can stand. In GW1e, you rolled 3d6 for Constitution and your Hit Points were 1d6 per point of Con. Average character has 10 Con and 35 Hit Points, and you died at 0. In GURPS the average person has HT 10, 10 HP and has a 50-50 chance of dying after taking 20 HP damage. For me, that's close enough - I didn't do anything fiddly with that. And because the Hit Points are basically unchanged, the damages done by Gamma World weapons need little modification. That said, I use a simplified version of GURPS guns, rather than the afterthought guns rules for GW1e as published in Legion of Gold.

  3. Oh, and one battle I lost: I can't figure out how to use d6 to roll on tables that as per Gamma World need 1d20, d% and so on. My GURPS Gamma World rules require a set of old-school polyhedrons (I think they were a monsters in MMII) in addition to GURPS d6. At least for now, I haven't solved that.

  4. Different approaches for different situations.
    If I have mostly non-interacting universes, I try to "run both systems": GURPS characters using GURPS skills to attack with Mekton II vehicles and damage values, using Mekton initiative/action rules; just the same, I'd do ArM arts, magic, lab and their improvement rules with otherwise GURPS characters.
    If there isn't such a clear divide, I tend to look at "what is the feeling I want to end up with" and devise GURPS rules to that end - I created GURPS versions of Protection from Evil, Floating Disk, Smite Evil, and so on.

  5. For most things, I want it to feel like the destination system. If I want things to feel like the source system, I'd play the source system instead. Sometimes it helps to think of what the mechanics mean in the source system instead of raw math.

    1. Make sense. I tend to have the same feeling - probably why I don't do any "how to convert AD&D monsters" rules. I'm not going to do math-to-math conversions anyway . . .

  6. I agree with Charles Saeger here. I'm running a Pathfinder Adventure Path in GURPS (largely because I wanted to strip out all of the level dependent escalation) and my rules modifications are really strongly focused on capturing "what does this mean to an average person in Golarion", rather than fidelity to either system.

    Spells that would kill or injure an average commoner--do that in my GURPS conversion. Monsters that can kill with a single bite do enough damage to do that to the average joe.

    But I also didn't work out a complete conversion, or a new set of GURPS rules, for everything. The players still pick out spells from Pathfinder--being assured that they will largely work the same way, in game play. I don't use Powers to write them up, or Magic to create them. They buy the spell, and it has those game effects.

    About the only things that I've deliberately GURPSified are things that I didn't enjoy about Pathfinder, such as a low level wizard/cleric/bard/etc. being able to cast precisely two spells per day, regardless of what else he did. Same with feats. I figured out how many points they cost, so that a feat that is terrifically useful isn't the same cost to acquire as one that's pretty marginal.

    It's been pretty great, because I didn't have to do all this conversion work at the front end, and because the players can still use the Pathfinder source material they own.

  7. I'm running a D&D 3.5 megadungeon in GURPS.

    I convert most things to GURPS rules, at different levels of resolution. A D&D Orc becomes a DF Orc, maybe with the Guard template. Knowledge (History) DC 25 becomes a History-4 check. A wandering monster table that uses a D12 becomes rekeyed to 2d6 or 3d6.

    I leave a few things as-is, if there's no equivalent GURPS rule and the D&D crunch is simple enough not to cause problems. The Ioun Stone of you don't have to eat remains the Ioun Stone of you don't have to eat -- I don't bother digging through books looking for the equivalent advantage or spell.

  8. When I convert to GURPS, I convert to GURPS - I'm playing GURPS in the world of (whatever). I will try to emulate the loose feel of things in the original (this guy is an agile fighter, that one is a heavy slugger) but I don't try to replicate in more detail.

    The one exception to this is my GURPS Torg conversion, where I've made several rule modifications to produce a more Torg-like feel: Possibility spending is basically Impulse Buys, but tweaked so that it works in a more cinematic way, for example.

  9. I use them for inspiration at best. GURPS tends to model things differently than many of the other systems out there, and a direct conversion is either impossible or becomes nonsensical in GURPS.

  10. Ive pulled in the rules for Essence and cyber/bioware costing Essence into a GURPS conversion of Shadowrun straight up. It is a feature setting with no easy counterpart in GURPS, and while it may not be the best way to deal with it, I sold it to my players by pointing out I wasnt charging points for cyber/bioware, it was just equipment...

    I do convert flavorful equipment from other systems all the time. A GURPS Adventure/Aberrant/Aeon conversion I did, I pulled in all the spaceships and mecha. A GURPS Living Steel/Aliens conversion pulled in all the guns and armor, with an actual formula for PEN to damage dice, because it kept the balance between gun and armor that was so important to that setting. And frankly, Ultra-Tech is very hard to pick and choose a balanced equipment list that way... Same issue with weapons vs Mecha DR for Robotech actually, and I used Spaceships to build those guys... actually worked pretty good.

  11. I use TFT and GURPS 3e monsters with minimal changes (adding Active Defenses to the former and dropping Passive Defense from the latter mostly).

    I've tried on multiple occasions to convert D&D monsters to GURPS but kept running into issues in that I wanted to list every _possible_ weapon a humanoid monster might have in his possession from his skill(s) of choice instead of just the most common ones and that most of the 3+ HD monsters just looked too powerful to me while 1 HD creatures looked too weak (since I've never had a good grasp on how D&D HP is supposed to work even when I played that; GURPS HP was perfectly intuitive and matched up with how I was used to interpreting the mechanics, I always just figured high-level videogame and D&D characters were basically brick supers in terms of toughness).

    As far as converting anything other than monsters, I usually find it more work than it's worth except maybe for spell lists and effects (but not costs, GURPS has a vastly different spellcasting resource paradigm than I'm used to anywhere else since it recovers somewhat with amounts of rest that can be reasonably worked between encounters on a given adventure).


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