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Armor Class: Ascending/Descending or other.
- Monster Stat Blocks – # appearing, AC, HD/HP, etc.
- Coins – Is it gp or sp standard and what is the ratio of one type of coin to another?
- Distance – feet/yards/meters vs. indoor/outdoor, etc.
- Combat Tables – Within OSR style rules, this shouldn’t change much, or so I think. In Delving Deeper the probabilities have been adjusted to be more statistically correct.
- Saving Throw Tables – How many types of saves are there? Some clones have opted for a single save.
- Turn Undead Tables – The scope and efficacy differ slightly, but what about the rolls to turn?
- Some might need conversion of treasure tables or experience point conversions.
- Crossing genres/rule systems, like the 1E DMG – six guns & sorcery with AD&D & Boot Hill, abilities need conversion.
- Thief/Assassin/Monk Abilities – Is this something that needs conversion? It depends on the rules system. [I like the d6 thief skill idea from a week or so ago. I’ll have to find the link for that article and link it here. I thought I saved it, and Google is giving me older stuff. I thought it was recent.]
- Morale checks – Something simple that doesn’t take too much calculation or rule consultation and slow play.
- Grappling – Again, something simple. This is more of which rules system does it best and use that for your game(s).
- Missile and Grenade Like Weapons – Something simple. Again, which rules system does it best.
- Feats – I’m not a big fan of feats as it takes away some creativity. Certain things might still need a roll, but roll against the ability that makes most sense, like a d20 or xd6 depending on how difficult. This part makes porting characters from one edition of D&D to another quite difficult from what I have read.
AC, Money, Distance, and Monster Stat Blocks look to be the big ones to be concerned about.
For monsters, the simplest is to convert the same critter to the same critter just using what the other rules use. It is only an issue for unique critters or your own design.
I have seen some tables here and there about conversion, but did not make a note of it and don’t recall if some PDFs of rules discuss this, or I read it somewhere online….
The two ideas I managed to find were for AC conversion, fairly simple, and monster conversion. With the release of 5e/Next, the focus is on converting 1E stuff to 5E. I am more interested in 1E and 0D&D and converting between clones, when there are differences.
For the most part 0D&D and AD&D and clones are close enough that there is very little need for conversion, other than armor class. I’m just interested in collecting any such tools that might be out there.
Has anyone put together a spreadsheet to aid in converting money systems between rules/campaigns/house rules? I haven’t tried to figure out the math for that, it may not be as easy as I think it should be.
[EDIT] Thanks to Alex Schroeder, of Alex Schroeder’s RPG Blog for reminding me of the OSR Rosetta Stone on the Hack & Slash blog, by Courtney Campbell.
[EDIT: 11/17/2014 – The Updated OSR Rosetta Stone that adds 5e and ACKS.]
Others are interested in RPG system converters, so I will link the ones I have found via Google below:
Armor Class: (This is the most commonly mentioned conversion.)
Old School Armor Class Systems Comparison (Tables)
Is the Main OSR Division Descending / Ascending Armor Class?
D&D 5e: Backward Compatibility and Combat Math
Ascending v. Descending Armor Class
I wade into the greatest OSR fight ever, several years late
Converting from Descending AC to Ascending AC
MONSTERS:
Conversion of LotFP (OSR) monsters to D&D Next Final Playtest rules
Stan Shinn’s 1e to 5e Combat Tracker
D&D 1E/3E to 5E Monster Converter
Anyone done a Pathfinder monster conversion sheet?
MOVEMENT:
Old School Movement Conversion Table
VISIBILITY:
ENCUMBRANCE: (Not so much conversion of encumbrance, but a discussion of an alternative system.)
“Inventory Slot” system in a “Survival Mode” game?
CHARACTER/NPC:
Are there any systems or recommendations for converting existing characters and NPCs to other versions?
What is the best way to convert a character to a system that uses feats? How do you decide what feats they get?
THIEF SKILLS:
Placeholder for the article on a d6 mechanic for thief skills that I read recently and as I recall, it was a recent article and not something I stumbled on that is a few years old.
OSR COMPATIBLE/STAT BLOCKS:
OSR Compatible Standard (Discussion)
A Simplified OSR Stat Block – On the Quest For the Perfect Game
Is D&D Next is Compatible With AD&D 1e “Out of the Box” – Wizards May be Saying So
Swords And Wizardry Is The Rosetta Stone of the OSR (There’s that Rosetta Stone usage again….)
Previous edition conversion to Next? Have you done it?
BLOOD & TREASURE (Discussion, mostly general of his RPG that takes a bit from other RPGs)
Please let me know if there is an article on a listed topic that is beneficial to add to the mix.
Also let me know if there is a category I left off and a link to a discussion of converting that category between systems.
NOTE: I am more interested about moving between 0DD/AD&D and clones, than 5e/Next. However, if there is a link that ties 5e to a specific OSR product that will enhance the OSR conversion discussion, please share. I have a feeling that 5e may end up being the cross reference point for a lot of people.