Turn Undead as Potency Formula

The Turn Undead chart can be refactored into a simple algorithm that compares the level of the Cleric and the targeted undead. Doing this flattens out a few quirks, like treating ghouls as being one step easier to turn than the chart makes them, but I'm fine with that since ghouls are pretty nasty.

	Turn Undead
Roll	Effect
7-8	Turn if HD = Level
9-10	Turn if HD = Level + 1
11+	Turn if HD = Level + 2

*Undead with fewer HD than the Cleric are turned automatically. Undead with 3 fewer HD than the Cleric are Destroyed automatically. Roll 2d6 to determine no. of HD destroyed.

Note: BX is a bit unclear on what happens if you encounter a mixed group of undead. I think they're assuming you are only encountering homogenous groups of randomly determined size, since they give an example of a Cleric smoking 3 mummies rather than a mummy and it's retainers. In that case, the procedure is the player rolls 2d6, and the DM tells them what it does.

This is a nice reference if you are adding extra undead not on the chart, but we can go further.

The Potency Roll

Matt Colville posted a video discussing his recently released RPG, Draw Steel. He describes the basic task resolution rules which are quite different from your average "I can't believe it's not D&D" d20 based game. Basic task resolution in the game is done on 2d10, and everything has a trinary result with fixed target numbers. Famously there is no missing, and no attack rolls either. There are only powers, and powers always do at least a little damage plus a rider effect.

In the design videos, Matt stated he strongly emphasized speed of resolution in combat. Therefore monsters don't make saving throws: when you make a power roll, you know what effect it's going to have (players roll to resist monster abilities). I think of this as a "unilateral" ability: you just do it, no back and forth needed like an attack roll or save vs DC.

Since monsters can't save, it might seem odd that the strength, speed or intelligence of a monster never influences the effect of a player's attack. Instead of adding a monster saving throw (which would make the abilities not unilateral) Draw Steel has a "potency check". It's a simple comparison of a target's ability score to a threshold; if they meet the threshold, they ignore the effect. The threshold is called a potency, and is determined by the level of success on the Power Roll used for that ability.

A character's Strong Potency = their highest ability score.
Average Potency = Strong Potency - 1
Weak Potency = Average Potency - 2
(In Draw Steel, abilities generally range from 0 - 5)

All Draw Steel abilities have three possible results. On a top tier result, you compare the Strong Potency with the specified ability of the target.
A middle result uses the Average Potency, and a bad roll means you use the Weak potency. On the image, the P < WEAK, P<AVERAGE, and P<STRONG entries indicate comparing the target's Presence with the various potencies of the PC. 

This means a player can just make their roll and say "If the goblin's Might is less than 3, they are knocked back". No back and forth needed. It's similar in principle to 4E's "attack vs defenses" model, although the potency check is only for the rider effect, not for damage.

I thought boiling everything down to one unilateral roll was interesting, since 5E has very little unilateral resolution rules. Everything requires the player to make a roll then check in with the DM to see if they made the DC (vice versa for saves). I started pondered roll to cast systems, partly because I've been playing Shadowdark and reading True Sorcery by Green Ronin.

I realized that early-model D&D actually has lots of unilateral mechanics; the attack roll is the only back-and-forth resolution rule:

x-in-6: DM sets number, player reports pass/fail
Roll-Under ability checks: player reports pass/fail
Saving Throws: Player reports pass/fail

Then I realized that that Turn Undead uses it's own bespoke system with 2d6 and 3+ results... hey, that kind of looks like a Power Roll!

If you squint, Turn Undead is kind of like a potency check, just using HD and 2d6...

This makes me think of using the Turn chart as a general purpose "power comparison" mechanic. You could relable it as a "power check" chart, and turn undead would just reference the general rule. A direct comparison of the power or force of two creatures could quite useful in your average BX game, such as if the Fighter wants to shove an Ogre, if the Wizard wants to play chess against another Wizard, etc.