Each class has a “Combat Target Number.” Anytime a character wishes to take offensive physical action against something, they roll a twenty sided die. If their roll on the d20 is equal to or higher their CTN, then the action succeeds. As each class levels up, their CTN becomes gradually smaller. Modifiers to the CTN are rare, which allows it to be very simple. A single number written on the player’s character sheet, which they must roll against.
Most characters will also have an Avoidance Score. This is typically a very small number, between -3 and 4. For most characters, their avoidance will be the same as their dexterity modifier; though if the character uses a shield, that will also add +1 to their AS. Again, modifiers to AS are rare, which keeps it simple. Any time a creature with avoidance is attacked, the AS is added to the attacker’s CTN.
Armor does not benefit a character’s avoidance score. Instead, it functions as a type of damage resistance. Each type of armor will have a die associated with it. As a simple example, lets say that leather armor uses 1d4, chain armor uses 1d6, and plate armor uses 1d8. Any time an attacker rolls a successful attack, they must then roll their damage dice against the defender’s armor dice. The value of the armor die is then subtracted from the value of the attack die, mitigating or even eliminating the damage dealt to the target.
My primary goal here is simplicity, which I think I’ve achieved. The player need not roll 1d20 + BAB + Strength + Weapon Bonus + Relevant Feat. They don’t even need to roll 1d20 + [Bundled Attack Bonus]. As silly as it might sound, taking two numbers and figuring out which is bigger is easier than taking two numbers and adding them together. I also like how the system keeps both the attacker and the target mechanically engaged. While determining the success of the strike, the player and GM need to communicate the CTN and the AC. While determining damage dealt, the player and GM are rolling dice opposed to one another.
You may have noticed that the CTN is to be used anytime “offensive physical action,” is taken. That’s because it would also be used similar to Pathfinder’s Combat Maneuver roll. The attacking player rolls against their CTN plus their target’s AS if they’re attempting to kick sand in their eyes, or disarm them, or grapple them, or whatever. Grappling in particular is traditionally complex and unwieldy. From 1st edition AD&D’s “Non-Lethal and Weaponless Combat Procedures“, to the system in D&D 3.X which was so complicated I literally kept a flowchart at the table at one point. Pathfinder’s combat maneuver system is a huge step in the right direction, but I think it can be simpler still.
When attempting a grapple, the attacker rolls against their CTN + their Target’s AS as normal. If they succeed, then they’ve got their hands, legs, tentacles, or whatever on their opponent. The attacker then makes a strength check (Roll 1d20. Equal to or under STR is a success, over STR is a failure). The defender may either roll a strength check, or a dex check, whichever they prefer. Whoever succeeds by more gets to pin/push/hold their opponent. If the two players tie, they are stalemated. If both players fail, success goes to the defender.
A basic example of play might proceed thus:
Fighter “I’d like to attack the orc. My CTN is 11.”
GM “The orc has an AS of 2, so you’ll need to roll a 13 or better.”
Fighter [roll] “A 15! That’s a success, so I’m rolling my damage die, 1d8.”
GM “The orc only has chain armor, so he’s rolling a 1d6 for defense.”
[Fighter and GM both roll their dice.]
GM “The orc rolled a 4.”
Fighter “That’s not bad, but I rolled a 6, so he still takes 2 damage!”
Rogue “Me next! I’ll get him with my throwing knife. My CTN is 14, so I need to roll a 16 or better here.” [Roll] “17, Success! Rolling my 1d6 damage die…”
[Fighter and GM both roll their dice.]
GM “I’m afraid the orc’s 3 beats your 2.”
Rogue “Fucking fuck. I wanted his gold. >:(”
Wizard “That really just leaves me. But my spells are gone, and my staff only deals 1d4 damage, so there’s a good chance I couldn’t hurt him even if I hit. I’m going to try to tackle him so the other players can hit him more easily next round.”
GM “Alright, you can try that. But you’ve got a CTN of 16, so you’ve gotta roll an 18 or higher to succeed.”
Wizard [roll] “I actually did it! I got an 18! Just barely!”
GM “Alright, but you’ve still gotta make your strength check. The orc is much stronger than he is agile, so he’ll be using his strength to oppose you as well.”
Wizard [roll] “Woo! I got a 10, that’s just under my Strength of 12!”
GM “Ah, but the Orc got an 8, which is way under his strength of 16. When you leap to tackle him he knocks you aside with his arm. You’re now sprawled on the ground behind him.”
There are a few complications to this system which I’ve omitted here. Both strength and dexterity do have a role to play, as do various positioning and circumstance bonuses and penalties. But this is the basic structure of the system, and I would be interested to hear thoughts on it.