Fight Smarter

In 3.5, I think the duelist applied his intelligence modifier to his armor class

Depends on the GM and context. Could be considered meta gaming because your char may/may not have access to the information needed. Intelligence DNE knowledge.
If your char is an alchemist/equivalent? I don't see why not.

>CREEEED

Fuck, after all these years why haven't I made this an actual ingame ability. Maybe even multiple characters, depending on margin of successess or whatever mechanics the game in question uses to grade skill rolls.

I feel like something like the rangers favored enemy should be INT based. Knowledge about how to fight an enemy, where to properly hit, is something you can learn and something you can apply in battle. If we assume that INT also means wit, a sharp mind, initiative and reflexes could also be based on INT.

Play OSR games where fighters aren't kneecapped by 2+Int skill points/level

Definitely some kind of counter-attack ability.
>Cunning Counter: Once per round as a free action, whenever an enemy adjacent to you makes a melee attack, you can make a basic melee weapon attack against it first.
>You use your Intelligence instead of Strength for the attack roll, and no stat for the damage roll. If you hit, the enemy's interrupted attack has disadvantage.
>For each previous time you have used this ability in the same encounter, you take a cumulative -1 penalty to the attack roll.
I tried to be very conservative here because I have no idea what else you want your INT-based fighter class to do.

The intelligence not to get into a melee fight when they have a ranged weapon available.

Actually, the more intelligent fighting strategy is to keep your opponents at range unless it's necessary to engage in melee or you have a much greater advantage over them when engaging in melee.

And the greatest fighting strategy is to not fight at all if you can help it, instead goading your enemy into depleting their resources through feints and misdirection, attacking them through means they have little ability to fight back against, and engaging in battle only when necessary or overwhelming advantage is afforded you.

If such knowledge exists in the setting, I'd say you just need the requisite materials, construction equipment, and knowledge resources. So you'd need to acquire the right books on how to manufacture every component, mix and acquire every chemical, and all the right workspaces to build it in. You won't be able to build a bomb out of an old helmet with an unrefined sulfur rock, a bag of sugar, and a short length of rope in the middle of a wet forest, but you could with access to a basic alchemical library, a basic foundry, and a store of basic reagents, limited to the supply of iron/chemicals/requisite knowledge on the topic, of course.

>If we assume that INT also means wit, a sharp mind, initiative and reflexes could also be based on INT.

Well, the act of moving is DEX for sure, but the awareness and realization that you are in a situation where you have to move can be based on intelligence, in the sense of a sharp mind, the processing power of the brain, to analyze a situation and react accordingly. You know, how you can consider someone slow, not in the sense of moving slow physically, but moving slow in the mind. Though one could argue that this is also a WIS thing.

You realize I could think of a way to make INT reasonably apply to every interaction because it DOES affect every interaction someone does if they have a brain, right?

Kinda? You need to learn everything, besides breathing. I guess most systems wouldn't consider such simple things like eating and shitting to be book knowledge. Do I need to read books on how to chop wood with an axe? Probably not, but you can train the actual act of chopping wood. Your average DnD off-shoot wouldn't consider such training INT-based. What about knowing where to attack a dragon, where the weak-spots are, in what direction you have to stab to hit inner organs? I bet you could write a book about these things, like you can write a book on how to hunt, which includes where to shoot at on different animals. This is applying book knowledge.

OP here. It could, depending on the system.

But I'm not talking about any specific system, I just want to have this discussion, so knock yourselves out interpretation-wise.

>Do I need to read books on how to chop wood with an axe
No, but you can optimize your efforts and minimize waste. The whole idea of process-improvement evolved from using scientific principles to make simple tasks more effective and efficient.

An idiot might walk all the way across the yard for his wood-pieces and waste time, while a smarter person could arrange his workspace in a way that saves himself time. He could time himself on each part of the task to find the most efficient way to do things.

At a sufficient level of intelligence, they are operating on a whole different level of efficiency to everyone else. Everyone else, friend or foe makes an Int save or spends their turn doing something mind numbingly stupid that seemed like a good idea at the time.

>COMBAT MASTERY
You've spent a lifetime studying every fighting style known to man. This broad base of combat knowledge allows you to instantly identify an opponent's movements and alter your own accordingly. While benign by itself, an accomplished martial artist with this skill is an exponentially more threatening opponent due to their ability to alter and improvise fighting styles on the fly.

But what does it *do*?

>identify an opponent's movements and alter your own accordingly

So...do what every entry-level fighter does. I get the feeling a lot of mana supremacists have never sparred.

Palladium has a character type called the natural genius. Basically it's combat bonuses give it a higher initiative and a chance to auto dodge attacks as the character knows what the assailant is going to do before it happens. The cool part is that it's not a mystic of psychic class which means it's attainable by anyone (cue Ultra Instinct).

The class has other features too which aren't related to combat but in my mind, I think this answers your question pretty well when talking about game mechanics and not player action/decision.

called shot (nuts)

muscle memory

>The intelligence not to get into a melee fight when they have a ranged weapon available.

What is holding your enemy by the belt buckle? What is maneuver warfare?

Getting into melee, historically, provides shock value. In firearms eras, close-range combat persists for better sensor data, speed, and surprise; which amounts to the same thing: accepting slightly higher risk to yourself, to impose dramatically higher penalties on the enemy, which sums up to lower risk to yourself and your side in the final calculation.

In D&D terms, fighters should have 6+ skill points, the ability to interrupt other players/classes actions, and be able to make intimidate checks as a free action.

In the system I run, dex and int play a much bigger part in melee combat than str. I use a variety of fighting schools (hard core hemafag fanboi) to give melee combatants a broader range than most rulesets. The different styles passively improve the fighter's skill, but by learning different styles and schools, the fighter gans bonuses against unschooled opponents and against styles for which there are counters. Knowing more schools and styles allows a fighter to adjust his methods to the weaknesses of the opponents, and its all Int based.

Also, since I play with a stamina and morale system, psyching out your opponent and recognizing when they're starting to slow from exhaustion also play a big part, and these are also int based.

From a mechanical balance perspective, combat modifiers derived from two basic stats each would have the advantage of mitigating outliers, because you would need to have both stats very high in order to max out a derived combat modifier, and conversely one very low stat might make a combat modifier only slightly below median.
Just off the top of my head, let's say:
>initiative: average of DEX and WIS
>weapon attack: average of STR and DEX
>magic attack: average of two mental stats depending on class
>evasion: average of DEX and INT
>fortitude: average of STR and CON
>willpower: average of WIS and CHA
Do not presume I'm talking about D&D specifically.

What system and do you have this all codified and written out so I can steal it?

Running away.