Updated: Nov 15, 2021
Whichever edition of D&D you’re running, it’s worth taking a look at other editions of the game to find cool ideas to use. For my AD&D Second Edition games like Dark Sun, here are some houserules inspired by other editions of the game.
Ascending Armour Class
This one is obvious, I suppose. In my games, Armour Class starts at 10 and rises from there. Hey, if it was good enough for Gamma World, it’s good enough for me. To convert from standard AD&D rules, subtract the AD&D Armour Class from 20 to find the ascending Armour Class. Done.
I do like THAC0. I’m not a hater. But this is a no-brainer, especially if you’re using ascending AC. So I convert THAC0 to an attack bonus – just subtract THAC0 from 20 to get the equivalent attack bonus. To make an attack, roll d20 and add the attack bonus and any other applicable modifiers. If the end result equals or exceeds the target’s Armour Class, the attack hits.
And actually, when it comes to monsters, I often don’t bother with converting THAC0 – I just give the monster an attack bonus equal to its HD. You can cap this at +15 if you want to keep the same limits that THAC0 had, or just let it go as high as you like if you want to make your players cry when they meet a high-HD dragon. Players should cry more, don’t you think?
B/X Ability Modifiers
I prefer the way the B/X (and BECMI) editions of D&D handle ability modifiers – there’s something about the distribution curve that I find elegant. Essentially, B/X gives a +1 modifier at 13-15, a +2 modifier at 16-17, and a +3 at 18. With a little tweaking, you can merge that with the standard AD&D ability score tables, which track scores up to 25. Here’s what that looks like for the Strength score, for example. And yes, I don’t use exceptional Strength either. Don’t you judge me!
Here's a pdf with all the adjusted ability score tables from my current Dark Sun campaign guide which I give to my players:
CMB/CMD from Pathfinder
Do you honestly like AD&D’s grappling rules? OK, fair enough. I don’t. I do like the Combat Manoeuvre Bonus/ Combat Manoeuvre Defence rules from Pathfinder though. I use these rules to handle most special manoeuvres in combat.
CMB equals a character’s attack bonus plus Strength To Hit bonus, plus a size adjustment (see below).
CMD equals 10 plus a character's attack bonus, plus Strength To Hit bonus, plus Dexterity Reaction Adjustment, plus a size adjustment.
To carry out a combat manoeuvre, roll d20 + CMB. If the result equals or exceeds the target’s CMD, the manoeuvre is successful. A CMB roll takes up one of the character’s attacks for that round.
CMB/CMD Size Adjustments
When assigning CMB/CMD to monsters, you can give them some extra bonuses to reflect high STR or DEX scores because 2e doesn’t give ability scores to monsters. Just eyeball what you think works.
Here are some common combat manoeuvres using this system:
A successful Disarm CMB check causes the target’s weapon to fly 2d6 feet in a random direction. A two-handed weapon requires two successive Disarm checks in the same round to be successfully disarmed.
A successful Grapple CMB check holds the target in place. The target can make a CMB check to break free. The attacker must make a Grapple check each round to maintain the hold. While two characters are grappling, both lose their Dexterity bonus to Armour Class.
With a successful Grapple check, the attacker can deal unarmed damage to their target, move them at half the attacker’s combat movement rate if the target is the same size or smaller, or continue to hold them in place.
The target cannot attack while grappled.
A successful Knockdown/Trip CMB check knocks a target prone. They must spend a round to stand up.
Sunder is an attempt to destroy an opponent’s weapon, armour, or other item. On a successful Sunder CMB check, the opponent’s item must save vs. crushing blow or be destroyed.
In Dark Sun, where weapons are made from various materials, the saves vary. Wooden weapons save as thin wood. Stone and obsidian weapons save as rock. Bone, chitin, or ivory weapons save as bone/ivory. Agafari weapons save as thick wood.
Metal weapons cannot be Sundered by weapons made from inferior materials. This gives metal weapons an added edge against weapons made from inferior materials.
You could also use 5e’s system of opposed ability checks/athletics NWP checks to get the same result. I just happen to like CMB/CMD.
Having something cool happen when you roll a natural 20 has been a popular houserule for years. D&D 5e grants double damage when you roll a natural 20, for example. I prefer something a little more restrained, so I use a rule where an attack that hits with a natural 20 automatically deals maximum damage for the weapon used, not double damage. Statistically, this averages out to about the same as rolling double damage, but eliminates those extreme results and doesn’t produce something you couldn’t get with a lucky damage roll anyway.
If the attack can only hit with a roll of 20, however, roll damage as normal – no critical hit is possible in such a case.
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