I'm new to D&D and am playing a 5e campaign as a Paladin with a focus on Dex rather than Str; I am considering multi-classing into Fighter to get the two-weapon fighting style, per some of the suggestions in this answer and associated comments. I also just like the idea of dual-wielding finesse weapons (perhaps a whip and a rapier) per the Rule of Cool.
Thematically, however, I would like my character to be interested in protecting others during combat whenever possible. So I like the idea of adopting the Paladin's protective fighting style, but since that style has no effect without a shield, the choice would be at odds with the dual-wielding I'd like to do.
One option would be to take the Sentinel feat, which is somewhat similar to the protective fighting style, except that it is offensive (providing an opportunity for attacks using a reflex action) rather than defensive.
What I really want is a game mechanic that would allow my character to defend others against incoming attacks without using a shield; to return to the whip example, perhaps this would mean using the whip, Indian Jones style, to interrupt an attacker before they can complete their attack. Ideally, I would like a feat or a fighting style that would do something like this:
When a creature within range of a melee weapon you are wielding attacks a target you can see (other than you), you can use your reaction to impose disadvantage on the attack roll.
This is just the protective fighting style but with a range determined by the weapon used to perform the defensive action and without the requirement for a shield. It also swaps "can see" versus "in range" requirements for the attacker and the target, since the idea is to somehow stop the attacker rather than to thrust a shield in front of the target. In particular, this prevents using the mechanic to do wuxia-style "blocking" of incoming projectiles.
My DM seems pretty amenable to variant rules and homebrew options, but he's also new to D&D, so neither of us have any experience making sure these sorts of options are well balanced and fair, nor do we know what other pitfalls there might be in making up the rules as we go along.
Is my proposed rule variant "broken" or unbalanced in some way? How do I decide whether this should be a new feat or an alternative fighting style? Is there any already-existing mechanic that accomplishes the same goals so that I can avoid having to write my own mechanic?
Best Answer
To find out, benchmark it
When balancing a new feature, you have to benchmark it against what already exists in the game. In this case, we have to benchmark it against all the other fighting styles. Let's assume a 16 Dex and ignore smite damage (which is constant regardless of the choice of fighting style).
Finding benchmarks
Defense: +1 AC
Build 1: Equip a shield and longsword. Overall +3 AC. DPS: 1d8+3 (7.5 ave) at level 1-4. 2d8+6 (15 ave) at level 5+
Build 2: Equip a greatsword. Overall +1 AC. DPS: 2d6+3 (10 ave) at level 1-4. 4d6+6 (20 ave) at level 5+
Dueling: +2 damage (one-handed rapier)
GWF: between plus \$\frac{4}{5}\$ and \$\frac{4}{3}\$ damage (two-handed greatsword)
Feat: Great Weapon Master (typical feat "tax"). Extra attack on a crit. Optional +10 damage per swing. No AC bonus. DPS: 2d6+3 (11.9 ave, with crit) at level 1-4, 4d6+6 (23.2 ave, with crit) at level 5+
Feat: Polearm Master (typical feat "tax"). Bonus action attack with a polearm. No AC bonus. DPS: 1d10+1d4+6 (15.3 ave) at level 1-4, 4d6+6 (24.1 ave, with crit) at level 5+
Protection: 1 reaction to impose DAdv with shield. +2 AC
TWF: +3 damage at level 1 (one-handed weapon)
Interpreting the benchmarks
When there is a feat "tax" that typically comes with the fighting style, I include it in the benchmark. Since the system allows for this synergy, having both must be in the realm of an optimized but balanced combination.
We see a trade-off mainly between AC and damage. Specifically, the benchmarks show us:
At a +3 AC bonus: DPS is 7.5 at level 1-4, 15 at level 5+
At a +2 AC bonus: DPS is 9.5 (w/o reaction) or 7.5 (with reaction) at level 1-4, 19 or 15 at level 5+
At a +1 AC bonus: DPS is 10 (no bonus action used) or 15 (bonus action used) at level 1-4, 20 or 22.5 at level 5+
Without an AC bonus: DPS is 11.9 or 15.3 at level 1-4, 23.2 or 24.1 at level 5+
When you create your new fighting style, check where it fits in the above list, and use your intuition where it doesn't quite fit.
Evaluating your Fighting Style
This is what you proposed as a homebrew:
This is a very versatile fighting style since it allows for any combination of weapons and shield, and might synergize with different feats. Let's examine each of those.
Build 1: Equip a shield and longsword. Feat: Shield Master. +2 AC. DPS: 1d8+3 (7.5 ave) at level 1-4. 2d8+6 (15 ave) at level 5+, reaction use
Build 2: Equip two rapiers. Feat: Dual Wielder. +1 AC. DPS: 2d8+3 (12 ave) at level 1-4. 3d8+6 (19.5) at level 5+, reaction use
Build 3: Equip a greatsword. Feat: Great Weapon Master. No bonus to AC. DPS: 2d6+3 (10.5 ave) at level 1-4. 4d6+6 (20.5 ave) at level 5+, reaction use
Build 4: Equip a halberd. Feat: Polearm Master. No bonus to AC. DPS: 1d10+1d4+6 (14 ave) at level 1-4. 2d10+1d4+9 (22.5 ave) at level 5+, reaction use
It comes out to be the same as the Protection FS when using sword-and-board, is weaker than TWF for dual wielded weapons, and is also weaker than GWF when using a greatsword or halberd.
This is good, because a FS that is too versatile risks being better than all the others. For example, if the Paladin could throw down a shield and pick up a second sword and suddenly be as good at TWF as someone with the TWF fighting style, but pick up a shield and suddenly be as good at defense as one with the Protection fighting style, then this feat would be better than either TWF or Protection.
Is it balanced?
It is very versatile, but damage-wise, it is weaker than most of the other options if it tried to copy them. But it is equivalent to the Protection FS when equipping a sword and shield. In this regard, it is stronger than Protection, such that given a choice between this homebrew and Protection, it is always better to choose this homebrew.
However, with regards to game balance, it cannot do something that any other fighting style cannot already do. On the whole, it does not break the game.