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The “Tens-Complement” system

One thing to know with houserules is that you’ve got to know when to walk away if the houserule is about a part of the game that’s not mainly under your purvey.

For example, rather than target20 or descending AC or the 3e/4E/5e style “d20 system”, I prefer the system where:

The defender’s AC is still ascending, but is generally ten lower than they are in 5e, like a skeleton has 3 rather than 13.
On the attacker side, the skill is descending. For example, a level three, dexterity 14 rogue would have an attack value of 7. It's the tens complement of what the hit bonus would normally be in tbe d20 system. But you wouldn’t have to think about it as the “tens complement” in a system that was build that way from the ground up..

To attack, you add these numbers together (so the rogue hitting the skelly would be 3+7=10), you note that number, and then for every attack vs the skeleton, you need to roll that number (ten in this case) or higher. Super fast, and gives the same outcomes as normal (dexterity 14 level three rogue would have a +3, and +3 vs 13 hits on a ten or higher).

Since things are written down this way on the sheet (for example, with this rule, your attack value of 7 is what’s listed, not the “+3”), it’s no extra calculation, it’s all already there at your fingertips. As you level up your own attack value gets lower. Saving throws used to work this way in D&D, and I wish attacks had, too.

The good thing is, well, it’s two good things. One, that you don’t need to add anything after the roll. You know instantly as soon as the dice hit the table. Super visceral. The game doesn’t pause mid-swing and asks you to do math. The math is handled before the swing. Second, and this is even bigger: you only need to do it once per monster. So rogue vs skeleton finds out that it’s “roll ten or higher” and then it’s that way to the end of the fight.

Love it. And, additionally, I like to roll the damage dice along with the to-hit die and just ignore ‘em on a miss. Fast just became faster.

It’s the ultimate Fortune at the End.

But, my players did not wanna do it that way (it’s been almost ten years since we had the convo) and ultimately this part of the game is theirs. They need to do it in a way they’re comfy with and they were unanimous about this 🤷🏻‍♀️

Sometimes when they’re rolling massive numbers of attacks, they subtract their hit bonus from the AC and it gives the same result (ten in this case), so, fair enough.

Since I mostly DM, or when I play it’s been OSR games like Labyrinth Lord, most of my experiences as a player of the d20 system has been with the Adventure System line of boardgames that I’ve played both with friends & family and as solo. There, I’ve tried both the “subtract hit bonus from AC” method (which is slow for me since I’m much worse at subtraction than addition) and noting the tens-complement of the hit bonus instead, and using that as above, but that has also been flawed since you need to roll so many different kinds of attacks in the Adventure System, both your own various attack cards and also the random monsters and traps that all pop up.

I’ve played 5e proper as a player like three times at most and all those times I did use this “tens-complement” method and it was awesome. It worked, unlike with the Adventure System, because in 5e you only have a small handful of attack bonuses, so I could write these down once and for all and be done with it, and when the GM said “14” I could hear that as “four”, and add my “roll-over value”.

I was using it as DM before we switched to the attack value system. This was early on when there was only a handful of monsters; I had made my own monster cards (by scraping the “Basic rules” PDF) that had the tens-complement noted. Once we had a ton more monster books it stopped being feasible.

One problem with the tens-complement system is that it’s a core system of a particular retroclone whose main creator tragically ended up making some pretty messed up political choices, siding with tyrants in the pursuit of liberty. I was out of the loop and clueless about that; I was only talking to him about game stuff and nothing else—he was always kind to me, not that that makes things any better for anyone who was hurt by the movement he involved himself in. But that guy did not invent the system; it’s been how saving throws have worked throughout all the early editions up through 2e and RC.

Fortune at the End

Attack value

Update: The “roll-extremes” system

Suldokar's Wake has a system where high and low are both good while middling are bad. This is usable with old THAC0 / descending AC rules: roll over your THAC0 or under the enemy’s AC to hit. Or roll over your own AC or under your enemy’s THAC0 to defend. I’m interested in this system. One huge advantage is how it’s out-of-the-box usable with older D&D books, giving the exact right probabilities (provided attackers always win ties, i.e. attacker wins if the roll is equal to the AC or to the THAC0). The tens complement system as outlined above does have some advantages still but I’m not so sure anymore.