Category Archives: OSR Converters

AD&D and Other Editions to 5e Conversion Methodology

A lot of common sense stuff here. If the monster in the module is in the Monster Manual of the rules you are converting to , use that. Other creatures can be substituted for others, or converted by bits and pieces of creatures with similar stats.

The reverse can also work, taking new creatures and adventures from 5e back to older editions or even other systems.


Metamorphosis Alpha – Random Plants & Animals

I posted a few days ago about my itch to dig into Metamorphosis Alpha. While starting to write this post, I realized that the Starship Warden is a megadungeon Innnn Spaaaaace. 17 levels plus the mid levels. Except like one may normally think of a dungeon, it does not have a clear 1st level equals easier. Particular locations double as both traversing the wilderness and dungeoneering. The inhabitants see themselves as travelling in wilderness, and the inter and intra level tunnels and so forth and the buildings on the habitation levels are the dungeons.

After getting that realization out of the way, on to random plants and animals.

On page 19 there is a procedure for Creating Non-Player Creature Mutations. This table focuses on animals, but is easily modified to substitute the plant mutations on page 16.

Begin by choosing the plant or animal type, then determining the number of generations for which a new mutation might be introduced. The rules say 1 – 10 generations, so a d10 easily handles that.

Then roll percentile dice for each generation to determine if a physical, mental, physical and mental, or no mutation for that generation.

Then roll 1-50, d100/2 and look at the physical and mental mutation charts, and if the roll is off the chart, there is a sub-chart for physical mutations, and for mental it always means higher intelligence.

It is simple to do the same procedure and substitute the plant mutations for the physical mutations..

Finally, there is a note that if there are two or three early generations with a defect mutation, that that organism was not viable and start over.

One need not limit themselves to the mutations available in the rules. Make up your own, or borrow from other games. There are enough options here that one need not expand unless a busy campaign with lots of players digs into a lot of options.

I rolled up one animal and one plant using this method.

Chipmunks are small and cute, so why not randomly mutate one and see what happens?

I rolled a 5 on my d10, for 5 generations. So next I rolled percentile dice for each generation to determine what kind of mutation. I came up with physical, physical, no mutation, mental, and physical. Next I rolled d50 (d100/2) for each mutation. In the first generation, I rolled a defect of skin structure change. Then I rolled heightened strength, heightened intelligence,and ended with a defect of anti-reflection, which means that a mental attack or defense has a 25% chance to backfire.

My interpretation of all this is that these are normal looking, if slightly larger chipmunks, that are physically strong, but can’t take a hit. They are smart so they know to avoid a physical fight. They have a crude mental attack ability that sometimes backfires, so they need a few more generations for this power to strengthen and for the defect to fade. These small creatures can get into nooks and crannies and might have arm bands and other useful, but small devices; and know how to use them. They don’t have the power of speech or telepathy, so communication will be crude unless a member of the party speaks chipmunk, or has telepathy.

For a plant, I did not initially specify a plant, but let’s say it’s a dandelion. I rolled 9 on a d10 for nine generations of mutations. I rolled five generations of physical mutations, one generation of mental mutations, and ended with three generations of physical mutations.

The physical mutations are: electrical or heat generation, symbiotic attachment for both the second and third generations, contact poison sap, a defect of an attractive odor, poison thorns, manipulative vines, and texture changes. The mental mutation is telekinetic arm. Since there is no heightened intelligence, there is no communicating with this plant. It merely seeks to eat to survive and reproduce.

It can generate an electric shock to stun or perhaps kill small prey. It has two methods of symbiotic attachment that allow it to control another creature. It’s manipulative vines are a refinement of it’s ability to make symbiotic attachments. It has a contact poison sap, like poison ivy, yet it has an attractive odor that puts it at risk of being uprooted before it bears seeds. It also has poison thorns that keep away unarmored creatures. I interpret this defect to be attractive to some creature or other plant that is immune to its poisons, thus making it vulnerable to specific animals. It must be armored to resist the symbiotic attachment, and have some way to minimize the effects of the telekinetic arm. This means that another creature needs to be generated to fill this niche. Perhaps the skin of this creature will allow the party to pass through an area of these plants with minimal difficulty. Or it could get all the plants in the area to gang up on the party….

The manipulative vines and telekinetic arm server to draw in nutrition from the surrounding area, whether plant or animal. Its poison sap is a weak digestive enzyme that with prolonged contact helps speed the breakdown of plant and animal matter into the soil. It has a structure change to its leaves that are rougher in texture to normal dandelions, but its characteristic bright yellow flower and white seeds remain. One thing it will do with its symbiotic attachments is control a creature to blow its seeds to reproduce. Like dandelions, unless the root is sufficiently uprooted, it can come back. Like regular dandelions, I can see there being a thick patch of these that are slowly growing and spreading throughout their area. Their symbiotic/manipulative vines have a length of 1d3 feet. Perhaps in a few generations the manipulative vines will enable these plants to move towards food, rather than merely draw it in. They could become mindless predators only seeking food when their current soil becomes used up.

It is easy to create new creatures and plants for a variety of purposes, both helpful, neutral, and dangerous. Some dangerous things could be harnessed to be of use, like poison glands, or explosive fruit.

I like how simple this was, and in a few minutes I had two new creatures. The GM can determine how long a generation is and how many generations for negative mutations to fade and something new result. Exposure to additional radiation and other environmental toxins might speed up the possibility of new mutations.

Since some levels are sealed off from others, one could easily generate different plants and animals using the same type as a starting point. One chipmunk on one level has descendants who are intelligent creatures, another remains mostly unchanged, while another might be a deadly and vicious predator.

Of course, as with any RPG, the GM is free to ignore or tweak any random roll, or just make up a creature to suit their tastes or needs.

Dungeon Desk Pad Kickstarter Update

Just got this update from Peter Ragan. 20 days just to get the funds, but he’s reliable so his print shop is all ready to go, just waiting on the money. I suppose all those planning a Kickstarter need to factor in 20 days until they get the money. So, barring something unexpected, this will deliver on-time.

#10 Kickstarter Funds Transferred
Posted by Peter Regan
The project funds hit my account this morning (not sure why it takes 4 days to transfer them on top of the 14 days they take to collect the funds) and I’ve just sent a payment to the printers. They’ve already set the print job up, which helps speed things along.
As soon as I get a firm delivery date I’ll add it to the comments here. I’ve got all the packaging supplies in hand ready to go. This week I’ll be printing the sticker sheets and ordering the A3 insert sheets.
I’ve had survey responses from all but three backers, and I’ll chase them up at the weekend.

Why Dice?

Adam Muszkiewicz told me at Marmalade Dog about a post he wrote just before the con on Why Do We Even Roll Dice? I finally had a chance to read it and he mentions dice drop table and their positions having as much meaning as their value. He also mentions several others who have recently made posts about such tables. He mentioned his article when he pointed out his all the dice table in his Metal Gods of Ur-Hadad, that I purchased at the con.

I wanted to mention Adam’s post and tie it back to my posts on Dice Drop Generators and All the Dice Tables.

I like these kinds of table and generators and want to link them together. I plan to create fixed pages that I can add all the links that I find for a central repository, for my own use as well as anyone else that is interested.

OSR Converters

When converting between game systems, what types of things need conversion?
  • 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


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 and Travel

Old School Movement Conversion Table


Visibility and Illumination

ENCUMBRANCE: (Not so much conversion of encumbrance, but a discussion of an alternative system.)

“Inventory Slot” system in a “Survival Mode” game?


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?


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 Logo

OSR Stat Block Revisited

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

Adventure Conversion

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.