u/ilmz

Hi there,

I have been working on a d20-adjacent homebrew and going back and forth on the classic armor debate. Figured I'd share where I landed because I'm not fully convinced yet and curious if anyone has tried something similar.

I have read extensively around the old dilemma of armor as AC or armor as DR and came to the conclusion that I am not sure I like either.

The DR problem is what's been bugging me. It looks fine on paper until you run the numbers. Take a character with 10 HP facing a 1d10 weapon. DR 0, they die in roughly 2 hits. DR 3, maybe 4 hits, fine. DR 5 and suddenly it takes around 20 hits to kill them. The curve just falls off a cliff because you're shaving off most of the average damage and even if you implement a minimum 1 damage per hit rule means you still technically get hit, just for almost nothing. An army of goblins becomes a joke. That's not what I want.

Plain armor-as-AC doesn't satisfy me either because once something hits you, the armor might as well not exist.

So here's what I've been turning over. Let's start from the assumption that HP isn't literal health, it's your trained capacity to stay in the fight. The HD 10 veteran doesn't have ten times the blood of a first-timer, they just have decades of conditioning that lets them roll with hits that would floor someone else. That is what HP scaling is modeling. Given that, armor should extend that capacity, not reduce each hit.

The idea I was implementing is that armor gives you a pool of bonus HP that drains before your real HP. Heavier armor gives more HP per Hit Die but reduces your Dex contribution to Defence, so you become easier to hit but harder to grind down. Full plate might go from +8 AC flat to something like +4 AC and 4 HP per HD. At HD 1 that's 4 extra HP, barely anything. At HD 10 that's 40, which is a real buffer.

The pool only counts for attacks that roll against your AC. Fireball, traps, poison, a fall: straight to real HP, no buffer. The reasoning is that when something targets your AC the whole active combat system is running, your body, your training, your armor positioning. When something bypasses Defence entirely that system never engaged, it's a different kind of harm entirely. Crits and sneak attacks still drain the buffer though, they just cost more from it.

Recovery: when you spend a Hit Die to recover, you refill the armor buffer too. Scaling is linear which is the main thing I like about it versus DR. Twice the HD, twice the buffer, no cliff.

What I'm not sure about: does tracking two HP totals actually add overhead at the table or does it play fast enough that it's trivial?

Should shields give a small buffer of their own? And does the "only Defence-targeting attacks" boundary hold up at the table or does it generate constant edge case questions? Do you have some edge cases in mind?

Has anyone run something like this?

Thanks a lot to everyone!

I've been working on a homebrew TTRPG called Swords & Magic, and one of its most distinctive features is how magic works. I wanted to share the system and get some honest feedback, especially from people who've tried something similar.

The core idea: spells are skills, not resources

There are no spell slots. Every spell you know is its own individual skill, and you can cast it as many times as you want. Two separate numbers define your relationship with a spell:

• Tier (0–9): the spell's power level, roughly equivalent to spell levels in D&D: cantrips are Tier 0, and the scale goes up to Tier 9. Higher tier means more powerful.
• Skill (0–20, though it can go higher): your personal proficiency with that specific spell. This is the number you roll against on your Casting Roll, so higher is safer. Improving a Skill costs experience, and higher-tier spells cost more to train.

So "how good are you at Fireball?" is a real, meaningful question with a numerical answer, separate from "how good are you at Magic Missile?", and a veteran caster with Skill 18 in Fireball is far less likely to blow themselves up than a novice with Skill 4.

Your spellcasting ability (Intelligence, Wisdom, or Charisma, depending on *how* you learned magic) determines which tiers of spells you can even learn: you need an ability score of at least 10 + Tier to pick up a new spell.

The two-roll system

Every casting involves two rolls:

1. A Casting Roll (d20) compared against your Skill in that specific spell: this determines whether the spell actually manifests
2. A Magic Attack roll (d20 + Skill + ability modifier), if needed, compared against the target's Defense score: this determines whether it hits

What happens when you fail

This is the part I'm most curious about. If your Casting Roll exceeds your Skill, you don't just fizzle. The gap between the roll and your Skill (the Failure Margin) determines severity:

• 1–5 margin: Fizzle. Nothing happens.
• 6–10 margin: Distortion. The spell goes off at half strength.
• 11–15 margin: Misfire. The spell hits the nearest valid target, friend or foe.
• 16–20 margin: Backfire. The spell hits you.

And if you roll a natural 20 on the casting roll, that's a Critical Failure Threat: you have to roll again, and if that also comes up 20, you black out entirely.

There's also an environmental layer: being grappled, in violent motion, or in bad weather penalizes your effective Skill, making failure more likely.

Metamagic

You can push any spell beyond its base tier to apply metamagic effects. Want to double the area? That's +3 tiers. Cast it as a bonus action (Quickened)? +4 tiers. Each tier above base reduces your effective Skill by 4, so pumping up a spell you're mediocre at is a real gamble. You need a high enough Skill that even after the penalty you're not at 0 or below, otherwise you can't attempt it at all.

Synergy

Spells within the same school or sharing a keyword (like fire or cold) provide cross-bonuses. Every two spells above Skill 5 in a school gives +1 to all others in that school. This rewards thematic specialization without locking you into it.

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The full rules are in the SRD at swordsandmagic.it: the Magical Skills page covers everything above in detail, and the full spell list is there too.

If you want to chat or dig in further, there's a Discord at discord.gg/ezrXx3uR3w

My questions for you:

• Does this system sound fun at the table, or does the failure probability feel punishing?
• Has anyone run a "spells as skills" system before (d100 games partly do this)? How did it play out?
• Is the two-roll casting process too slow in combat?
• Any obvious exploits or balance problems jumping out at you? Would love to hear from people who've wrestled with similar design problems.

Would love to hear from people who've wrestled with similar design problems.