So this is applicable to 5E, Castles & Crusades, Shadowdark and other D&D-related games that use stat-based saves.
AD&D (and its retro-clones) use the following saving throws:
- Paralyzation, Poison or Death Magic
- Petrification or Polymorph
- Rod, Staff or Wand
- Breath Weapon
- Spell
So we have five save types verus six stats. And, worse, they don't break down evenly. At a glance, both Breath Weapon and Petrification saves should probably both use Dexterity, for instance. Poison/Death Magic sounds like Constitution. And why are Rod/Staff/Wand and Spells different save types?
The first thing to keep in mind is that 1e AD&D assumed that different classes would resist different attack forms using different methodologies, This meant that Gygax was making a statement about the effectiveness of not only different attributes against different types of attacks, but also the relative effectiveness of willpower, fortitude, luck, divine protection, and knowledge of the arcane arts - that is to say the sort of gifts that leveling up in a class would bring you. But even more complexly, the table assumes that as characters leveled up the relative effectiveness of a particular approach would change.
One approach would be to look at the class that was assumed to best resist a particular and ask what is that class actually good at, but I think this approach is almost too complicated to be useful. It's going to be very hard to translate a table that assumes bonuses from ability scores are secondary to success into one that assumes that they are primary to it.
So, I'd do something like everyone saves versus everything on a 15. All classes get a bonus equal to 1/2 their level rounded down.
I think I would break the five out into six and do some rearranging as to what attribute effected your chance of saving successfully, like so:
Death Magic - Charisma
Poison, Paralyzation, Petrification and Polymorph - Constitution
Rod, Staff, Wand, Ray and Missile Type Spells - Dexterity
Breath Weapon - Strength
Charm & Illusions - Wisdom
Other Magic - Intelligence
Additionally, I'd try to capture some of Gygax's original thinking like so:
Fighters: +2 bonus to STR and CON saves
Thieves: +2 bonus to DEX and INT saves
Clerics: +2 bonus to CHR and CON saves
Magic-Users: +2 bonus to INT and WIS saves
That's mostly pretty good except arguably, M-Us were also good at DEX saves under the original rules and we'd need to address whether this is a balance issue, and we now have so many exceptions to the 'Spells' category it's not clear what's left in it. The two questions are related in that if not much is left in INT saves it doesn't hurt to give M-U's "DEX" saves either.
10th level Fighter with the array 18 Str, 11 Int, 12 Wis, 14 Dex, 14 Con, 9 Chr would have the savings throws of approximately (depending on how you did stat bonuses):
Death Magic: 11
PPPP: 6
Rod/Staff/Wand: 8
Breath Weapon: 4
Charm/Illusions: 9
Other Magic: 10
10th level Thief with an array 12 Str, 14 Int, 9 Wis, 18 Dex, 14 Con, 11 Chr would look something like:
Death Magic: 10
PPPP: 8
Rod/Staff/Wand: 4
Breath Weapon: 9
Charm/Illusions: 11
Other Magic: 6
