Here my D&D players hunt a Barovian witch on a BattleTech map.

 It would be a shame to not use all your toys in this situation simply because you reasonably limited your campaign to one rule system…
If you’re like me and play multiple games from different companies, you probably have multiple products for different game systems lying around. Perhaps you have maps from the Conan board game by Monolith, some model train terrain, and D&D 5e dungeon tiles; however, you’re currently trying out the Pathfinder 2.0 Playtest rules, but you also want to run that Warhammer Fantasy Roleplay adventure book Lure of the Lich Lord that you impulsively purchased two years ago. It would be a shame to not use all your toys in this situation simply because you reasonably limited your campaign to one rule system; this is why we need conversion rules. Now I’m not necessarily talking about creating a homebrew that’s a hybrid of multiple rule systems. I’m talking about taking a product designed for a different table top game than the one you’re currently playing and giving its features meaning within the rule system you’re currently playing.

I discovered a method to creating conversion rules that I can demonstrate to you by explaining how I made my conversion rules. 
I did this with BattleTech terrain maps throughout the entirety of running D&D 5e in The Storm King’s Thunder and The Curse of Strahd adventure books. Both of those campaigns have great dungeon maps or indoor maps where combat may take place, but those maps required time for me to draw or buy digitally before game day. What’s more, most of the combat spontaneously occurred outside because my players were traveling murder hobos, and I wouldn’t let them fast travel. My players traveled regularly from one edge of the world map to the other. I rolled for random encounters for every half hour of game time. As a DM, I couldn’t prepare for where a wilderness terrain combat would take place or even what kind of wilderness the combat would take place in. So, my large collection of BattleTech map sheets came in handy. Those map sheets contain a hex grid on top of terrain for all kinds of wilderness, but they’re made and labeled for a very different rule system from D&D 5e. This necessitated my creation of conversion rules for the BattleTech map features to D&D 5e rules. I discovered a method to creating conversion rules that I can demonstrate to you by explaining how I made my conversion rules.

How To Make Conversion Rules, Step 1

Start by analyzing the kind of features you’re converting over to your current campaign’s rule system. They will likely be for combat or role play. I used my terrain based BattleTech map features for combat, so my conversion rules had to do with combat and how terrain affects combat. Then, gather data on what your current campaign’s rule set contains to deal with the kinds of features you’re converting. In my case, terrain affects combat in D&D 5e by adding movement penalties or altering attack modifiers. The concepts D&D 5e has to deal with terrain and combat include difficult terrain, half cover, three-quarters cover, climbing, and swimming. Learning those rules thoroughly and labeling them for quick reference was important for me, and it is important for you to do the same with whatever system you’re working with before moving on to the next step.

How to Make Conversion Rules, Step 2

This BattleTech map held a battle between Columbus and Toledo in Ohio’s ongoing BattleTech civil war. Notice the different hex terrain types that I converted over to D&D.

The next step requires identifying the converting features. For example, BattleTech maps yield an abundance of terrain: level 1 hills, level 2 hills, level 3+ hills, light woods, heavy woods, depth 1 water, depth 2 water, depth 3+ water, and rough terrain. At least know the definitions of your converting features. In my case higher numbers represent higher level hills or deeper water depths; light woods contain few trees with less cover; heavy woods contain more trees with great cover, and rough terrain simply contains some kind of debris.

How to Make Conversion Rules, Step 3

Compare your current rule system’s concepts from step 1 to the features’ definitions in step 2 and hope everything lines up somehow. Fortunately for me, things lined up nicely.

Walking onto any non-clear terrain hex on a BattleTech map in D&D 5e simply converts to difficult terrain for movement purposes. It’s also intuitive to see that a D&D 5e character in a light woods hex should receive half cover, and a character in a heavy woods hex should obtain three-quarters cover. A character in water of a certain depth needs to swim and traversing hexes with a level change of a certain height requires climbing.

Once you see what generally needs to be done, write down the specifics and really get into the nitty gritty of everything. Be prepared for the worst from your players. Give them a page or two of the conversion rules that relate to their character, and give them the full rules you made also. If you made your conversion rules well, everything should be close to the rules as written in your current campaign’s rule system.

Check out my conversion rules if you desire exemplification of what I mean by, “getting into the nitty gritty of everything”:

I also made a YouTube video over my conversion rules that you can check out here:


On The Importance Of Writing Down Your Conversion Rules

Writing down rules can be a pain. I didn’t write down my rules at first. This led me to inconsistently apply how things in my world worked. My players did not enjoy that. One week moving about my world worked one way, the next week a different way. They couldn’t use their past experiences to help them plan out what to do in the future, and I want my players planning their move before their turn comes up. All that changed after I wrote my rules down and handed my players a page over how their characters may move across the BattleTech terrain with their D&D 5e characters. The game ran faster. If I made a mistake, a player could point to a sentence in my rules and remedy the mistake; this is always nicer than hearing a player complain: “Hey, that’s not how it worked last week!”

See the full witch hunting ground, provided by one of the latest BattleTech maps. I used modular terrain because the witch prepared some high level illusion spells, but my D&D players didn’t know that.

Do you have any conversion rules that you want to make? Have you made any conversion rules? What other different toys could we combine together in a campaign? Let’s talk about such things in the reply section below.