Friday, March 8, 2024

Deathtrap Lite: the Keep on the Borderlands Principle

When I set out to build Deathtrap Lite, one of the core ideas I had in designing the game was that I wanted it to be compatible with most TSR-era D&D modules and OSR adventures on the market, while still being mechanically distinct.

Inspired by a video from Questing Beast, I made one of my rubrics "Can I still play The Keep on the Borderlands with this?" If the answer became"No." I adjusted until it could.

The whole point of the exercise was to make a game that was built on a particular mechanic, just to see if I could: a player-facing one based on an evolution of the Taps & Tankards simple skill system and Stephen Smith's World of Weirth adjustments to it, but what would be the point if my readers, who are mostly an OSR crowd couldn't use it, after all?

I also was curious to see if there is a market for OSR-comaptibke non-D&D games.

Making Combat Work

To that end I found ways to integrate hit points, and use AC to generate a monster's major combat facing stats. 

In combat, a Deathtrap Lite PC rolls using the Close Combat or Ranged Combat skill to attack, They get a bonus for having the Lucky Break or Mighty Deed of Arms skills. And a penalty based on the monster's Armor score. I provide a quick and dirty rmtavle for converting OSR AC into Deathtrap Lite Armor.

To avoid getting hit, PCs make a saving throw with a bonus based on the Close Combat, Lucky Break, or Mighty Deed of Arms skills if the PCs have them (This makes Warriors who have two of those really good at not getting hit, compared to other PCs.) As well as a bonus for wearing armor if they choose to do so. Shields offer a considerable bonus if a PC has a solid Close Combat skill. There is a penalty to this roll based on a monster's Hit Dice, which can be quite substantial at higher levels.

I included a "Wear Armor" skill in the game. If a PC is trying to do athletic tasks or move quickly while in armor the GM may choose to make them use that skill instead of something like Stealth, Athletics, or Acrobatics, making it a liability, and giving Warriors an edge, as they are the only ones trained in it. I felt this made wearing armor helpful, but perilous, without needing too much crunch. (Wear Armor also can provide a bonus when trying to survive the cold.)

The Armor rating affects rolls very differently to AC in OSR games, and combat is resolved differently, but at the end of the day, the mat, especially at low levels gives you very similar results. 

For trained combatants, the to-hit probabilities don't stray very far from the numbers in D&D: PCs are going to hit an unarmored foe 50% of the time and a moderately-armored one about 25% of the time, with warriors starting better than that. Tougher opponents are going to be harder to hit. Noncombatants will only hit unarmoured opponents around 25% of the time, and be nearly useless against armored or well-trained foes.

As the game goes into higher levels (slowly) PCs are going to hit does a bit more often than in D&D, but also get hit a lot more often, too. I did this quite on purpose: making stealth and cunning more rewarding, and brute-force combat an even bigger mistake.

So, despite being mechanically different it can use the existing stat blocks with only one adjustment and some adjudication.  Keep on the Borderlands compatible? Check.

Hit Points 

For combat's purposes, I included hit points, as they are a major factor in OSR games, and throwing them out entirely would be foolish. They do stand out as a proud nail in the system.

PCs get a fixed rate of hit points both at the start and while leveling up. I am generous with low-level PCs because Defense rolls can be hard, especially for Mages and Knaves.

For this reason I also included damage dice and monster hit dice, with a monsters attack rating being equivalent to its hit dice at low levels or slightly lower once hit dice get over 7 in order to conform to the curve of the OSR.

Once I had completed my rough draft of Deathtrap Lite, I set out to create a cohesive system that didn't include this one incongruous element. This was why I created Midnight Zone: it was an attempt to create a purer iteration of the system. But so long we are trying to keep Deathtrap Lite compatible with Keep on the Borderlands, 

As it is, the monster stat block in Deathtrap Lite should look pretty familiar to OSR players, and the translation pretty easy to make. It has Hit Dice, an armor value, attacks, etc.

Overall, most encounters in a classic module are easily converted.and it can be done on the fly pretty fast once you have a grasp of the system. 

My Big Omission

When I started building Deathtrap Lite, I decided to tie it to a campaign setting that added elements of Steampunk and dark fantasy to the game. I conceived of a fantasy world where humans had repudiated the gods and destroyed most non-humans. I drew a lot of my inspiration from Simon R. Green's Nightside books.

In creating my system and my setting simultaneously, I lapsed in one place when planning for OSR compatibility: I omitted clerics from the game. The Knave and Mage classes are capable of healing using alchemy to make addictive healing draughts, which is an acceptable substitute if you think of clerics as healers... But they are much more than that.

Missing the Cleric option means there are some bad guys you might have to reinvent on convert on the fly. And it makes it needlessly harder to play in another setting.

This is something I plan on fixing with a free download this month, and will include in my complete edition of Deathtrap Lite later in the year.

To tie it back to my exervise: Given the proliferation of evil clerics in Keep on the Borderlands,  this is a glaring omission, that requires some attention. 


I followed in the footsteps of Lamentations of The Flame Princess and moved the game to a silver standard. This is an aesthetic choice that I feel adds some grit to the setting.  With treasure disconnected from levelling except by paying for trainers and carousing , whether a GM converts the coins down to silver or leaves them as gold is their own call. Thus it doesn't stop people from playing Keep on the Borderlands with it.


I have three magic systems for Deathtrap Lite in the game to offer some options. One of them simply uses vancian spells, and I have a hyper-compressed spell list in the book. For NPC spellcasters this option allows the GM to use NPCs for other systems without making any serious adjustments,  although having something like Mike Evans' Concise List of OSR spells handy for ones I may have omitted is helpful. I tried to include equivalents for almost all of the magic user spells in B/X in there, with some favorite extra goodies from Lamentations of the Flame Princess and Knave as well

NPC spellcasters can just use this simple system without any real conversion needed. Meanwhile major NPCs in your campaign and PCs can use the more flexible systems if you prefer to make magic seem stranger and more wondrous.

Using two systems in this case allows smooth integration of NPCs made in other games while allowing the flexibility I wanted in magic to have for the PCs. So, the spelkcasters in Keep on the Borderlands won't require any sweat from the DM to run. Check.

Using Donjon and Modules

I've used Deathtrap Lite to run adventures generated by Donjon for AD&D, and run them in Deathtrap Lite with few hitches. As have I run my module Queen of Decay. I would love to hear about anyone else's experiences running them.

One of my biggest fans and reviewers on DTRPG, Bob V.G. has run Dungeon of the Week #1:Scattered Chambers of the Leper One, with it and reported a good experience

This is promising,  as it means, in principle Keep on the Borderlands ought to work. 

Why Did I Do This, Again?

I do believe that this is a great principle for designing any game you want to offer the OSR crowd. After all, it means tying your game not just into the material you can produce, but the material of a legion of other creatives spanning 50 years. And one of the things I hope Deathtrap Lite will eventually prove is that you don't need to use D&D's engine to offer an OSR experience... as long as you keep checking in.

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