Is this verstatile fighting style and feat combination well balanced?

Question

(original title: "How to artfully min-max the hell out of this verstatile fighting style and feat?")

So, given all the answers to my previous question, we have come up with what we think hope is a balance fighting style, and an accompanying feat, for fighting with versatile weapons.

Note from the chat:
I would like to know if the combination of this fighting style and feat is balanced in general; not if it balanced for specific builds. Just like Two-weapon fighting was not written for a specific build: it is a generally available fighting style, that can be used by different builds. The same goes for Dueling, and Great Weapon Fighting.
I asked the question in this same light.

Background

Because we feel fighting with a versatile weapon, seamlessly switching between one- and two-handed wielding, is an iconic style of fighting, that is under-represented in D&D. This is because the rules favour either sword-and-board or great-sword wielding brutes. Yes, you can wield a longsword with either Great Weapon Fighting or Dueling, but we feel that both fall short on the versatile-part.

So, we intend this fighting style to be an alternative to the existing melee fighting styles (Two-Weapon Fighting, Dueling, and Great Weapon Fighting), that it provides flavourful option, to those character that it appeal to, without disrupting the balance of the existing rules.

Fighting style

Versatile Fighting

When you are wielding a versatile weapon with which you are proficient, and no other weapons or shield, you gain the following benefits:

• You gain a +2 bonus to damage rolls¹⁾.
• When another creature hits you with a melee attack, you can use your reaction to add your proficiency bonus to your AC for that attack, potentially causing the attack to miss you.

Feat

Versatile Mastery

When you are wielding a versatile weapon with which you are proficient, and no other weapons or shield, you gain the following benefits:

• When you wield your weapon with one hand, your weapon has the reach property.
• Before you make a melee attack, you can choose to take a -3 penalty to the attack roll. If the attack hits, you can make an additional melee weapon attack, with the same weapon, as a bonus action.

Design intentions

We wanted a set of rules that are easy to understand, and easy use. The rules should provide an interesting option to character classes with access to fighting styles, that is different enough in flavour to merit its existence. It should be strong enough to be a valid, competitive choice, while at the same time not so strong that it overpowers the existing fighting styles.

However, D&D has many rules that seem balanced enough on their own, but, when artfully min-maxed, can be turned into a game-breaking monster.

We feel relatively confident about the Versatile Fighting fighting style on its own being fairly balanced, and less certain when the Versatile Mastery feats comes into play.

So, my questions are:

• Is this fighting style, and the accompanying feat balanced?
• Can these rules, when combined with other rules, become too strong?

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Appendix I: Average Damage per Round, formula

The Average Damage per Round without the Versatile Mastery feat is rather straight forward, so I'll not explain it here. The Average Damage per Round with the Versatile Mastery feat is rather more complicated, and can be calculated as described below.

Please refer to MannerPots's answer, for a complete explanation of the math involved. What follows here is a slightly adapted version of the formula given in his answer:

Let \$n\$ be the number of regular attacks, \$p_n\$ be your chance to hit, \$p_p\$ be your chance to hit with -3 penalty, \$p_c\$ be your chance to crit, \$d_n\$ be your damage on a normal hit and \$d_c\$ be your extra damage on a crit.

Then the expected damage of a normal attack is \${p_n}d_n + {p_c}d_c\$.
The expected damage of an attack with a -3 penalty is \${p_p}d_n + {p_c}d_c\$.

Then the total Average Damage per Round is:

$$\sum_{i=0}^{n-1}(1-p_p)^{i} \left({p_c}d_c + p_pd_n + p_p(n-i)({p_n}d_n + {p_c}d_c) \right)$$

Appendix II: Average Damage per Round, pre-calculated

Table 01: Versatile Fighting (1d10)

Hit probability	1 attack	2 attacks	3 attacks	4 attacks	5 attacks
5%	0.850 hp	1.700 hp	2.550 hp	3.400 hp	4.250 hp
10%	1.425 hp	2.850 hp	4.275 hp	5.700 hp	7.125 hp
15%	2.000 hp	4.000 hp	6.000 hp	8.000 hp	10.000 hp
20%	2.575 hp	5.150 hp	7.725 hp	10.300 hp	12.875 hp
25%	3.150 hp	6.300 hp	9.450 hp	12.600 hp	15.750 hp
30%	3.725 hp	7.450 hp	11.175 hp	14.900 hp	18.625 hp
35%	4.300 hp	8.600 hp	12.900 hp	17.200 hp	21.500 hp
40%	4.875 hp	9.750 hp	14.625 hp	19.500 hp	24.375 hp
45%	5.450 hp	10.900 hp	16.350 hp	21.800 hp	27.250 hp
50%	6.025 hp	12.050 hp	18.075 hp	24.100 hp	30.125 hp
55%	6.600 hp	13.200 hp	19.800 hp	26.400 hp	33.000 hp
60%	7.175 hp	14.350 hp	21.525 hp	28.700 hp	35.875 hp
65%	7.750 hp	15.500 hp	23.250 hp	31.000 hp	38.750 hp
70%	8.325 hp	16.650 hp	24.975 hp	33.300 hp	41.625 hp
75%	8.900 hp	17.800 hp	26.700 hp	35.600 hp	44.500 hp
80%	9.475 hp	18.950 hp	28.425 hp	37.900 hp	47.375 hp
85%	10.050 hp	20.100 hp	30.150 hp	40.200 hp	50.250 hp
90%	10.625 hp	21.250 hp	31.875 hp	42.500 hp	53.125 hp
95%	11.200 hp	22.400 hp	33.600 hp	44.800 hp	56.000 hp

Table 02: Versatile Fighting (1d10), with Versatile Mastery

Hit probability	1 attack	2 attacks	3 attacks	4 attacks	5 attacks
5% - 45% 2)	...	...	...	...	...
50%	6.409 hp	12.683 hp	18.870 hp	25.001 hp	31.094 hp
55%	7.515 hp	14.664 hp	21.593 hp	28.391 hp	35.110 hp
60%	8.679 hp	16.681 hp	24.311 hp	31.736 hp	39.048 hp
65%	9.900 hp	18.725 hp	27.013 hp	35.031 hp	42.916 hp
70%	11.179 hp	20.788 hp	29.691 hp	38.276 hp	46.718 hp
75%	12.515 hp	22.861 hp	32.339 hp	41.471 hp	50.463 hp
80%	13.909 hp	24.936 hp	34.954 hp	44.619 hp	54.160 hp
85%	15.360 hp	27.003 hp	37.531 hp	47.724 hp	57.817 hp
90%	16.869 hp	29.055 hp	40.070 hp	50.792 hp	61.442 hp
95%	18.435 hp	31.082 hp	42.571 hp	53.829 hp	65.041 hp

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^{1) To avoid confusion, I will not change the wording of the question. However, as stevenjackson121 already suggested, this bonus is intended to only apply to the versatile weapon in question. So this bullet point should read: "You gain a +2 bonus to damage rolls with that weapon."}

^{2) It only makes sense to attempt to trigger the bonus attack, for a hit probability of \$50\%\$ or higher.}

Answer 1

There is at least one Exploitable Edge Case

There are several minor, but important differences in the wording of your fighting style and the accompanying feat compared to official options that seem exploitable. I recommend going over the language used in official feats and trying to match it as closely as possible to prevent cheese unique to your new fighting style and feat.

Versatile Fighting For Monks and Spellcasters

Dueling says

When you are wielding a melee weapon in one hand and no other weapons, you gain a +2 bonus to damage rolls with that weapon.

While Versatile Fighting says

When you are wielding a versatile weapon with which you are proficient, and no other weapons or shield [...] you gain a +2 bonus to damage rolls.

As written, this would apply to a monks unarmed strikes made with the free hand or another body part, or spells/cantrips. Both can make multiple attacks per round (Scorching Ray, Eldritch Blast, Flurry of Blows, etc.) that would provide a larger benefit than intended.

This is especially important because Monks and Gish characters are probably going to be attracted to the feat in the first place (the ability to gain defensive benefits without a shield is good for both, and being able to switch between "focus + sword" or "2h grip on sword" is a possible gish option).

Versatile Mastery For Glass Cannons/Gishes

This isn't necessarily an exploit, but this feat will probably not support the playstyle you intend. Characters will not likely utilize both 1 handed and 2 handed options against the same opponent (either it's an opponent they're fine duking it out with using 2h from 5 ft., or they're an opponent that needs to be kited and killed with only 1h).

This may even be attractive for characters who never intend to use the 2h option. Reach is usually only available on martial weapons, and even among those only the Lance (which has its own drawbacks), Whip (which has terrible damage), or weapons with both the two-handed and heavy property have Reach. Introducing a way to get Reach on simple melee weapons wielded in one hand makes the trait vastly more accessible, and may be worth a feat for certain builds.

A Rogue would strongly benefit from the ability to use the Sun Blade for example, which has both Finesse and Versatile, to reliably sneak attack from 10 ft away and then retreat while reserving their bonus action for Steady Aim (If mounted), or a subclass feature (like Use an Object for Thief).

Outside of reach, BladeSingers (as one example) can use versatile weapons but can never attack with 2h or use shields, and may just always hold a focus in the off hand. This feat might still be worthwhile to pick up just for reach.

Different Enough to Merit Existence?

Great Weapon Master gives the opportunity to earn a bonus action attack on your turn, and also gives the opportunity to sacrifice hit chance for damage. The current 2nd bullet of Versatile Mastery basically rehashes this same tradeoff.

Similar to Great Weapon Master, the feature will only be useful against enemies you already need a 20 to hit (extremely high AC) or enemies that are very easy to hit (low AC) and poor in the middle.

I recommend trying to give a bonus that currently doesn't exist in melee, such as the to-hit bonus present in Archery Fighting Style, which is much more effective against mid-range ACs and least effective against extremely high ACs (which can only be hit with a 20 regardless) and very easy ACs (going from 80% to 90% changes DPR by a much smaller percentage than going from 25% to 35% chance to hit).

Tying this bonus to explicitly changing stances will help it remain a flavorful option for a specific playstyle, rather than being a feat pure 1h characters take to get a unique benefit more than actual versatile characters.

Recommendation

Clean up the language for the fighting style so the damage bonus only applies to the weapon in question.

For the feat: at minimum, add a bonus for either switching or add a bonus that's only accessible when attacking with 2h. Maybe the initial hit in the second bullet must be made with 2h to get the bonus action attack, or maybe you don't provoke opportunity attacks from enemies you attack with 2h.

I'd consider a full rework more along the lines of:

Versatile Mastery

When you are wielding a versatile weapon with which you are proficient, and no other weapons or shield, you gain the following benefits:

• When you make a melee attack using 1h, subsequent melee attacks with the same weapon on this turn using 2h have +2 damage for the rest of the turn.
• When you make a melee attack using 2h, subsequent melee attacks with the same weapon on this turn using 1h have +2 to hit for the rest of the turn.
• If you miss a melee weapon attack, you can make an additional melee weapon attack with the same weapon, as a bonus action.

The "bonus attack on miss" helps make damage output more consistent (contrasted with the swingy all or nothing nature of GWM damage output) and ensures the first 2 bullet points can occasionally be used by any character even before extra attack. Misses will happen frequently against tough opponents from level 1 all the way through level 20, especially for martials who make a high number of attacks.

The first 2 bullets offer two ways to structure your turn, roughly: a higher damage mode for easy to hit opponents, or a higher hit chance mode for other opponents. The +2 to hit is likely to be stronger most of the time, and that's good because that differentiates the feat most from other melee options (and even from sharpshooter) by prioritizing consistency. The +2 damage is more of a flavorful addition and to add versatility.

Ensuring the benefits are tied to stance changes also ensures edge cases involving pure 1h characters or pure 2h characters abusing the feat are prevented entirely.

Answer 2

It seems a little strong, but not outright broken, but you won't really know without playtesting.

Starting with the fighting style, the damage bonus is the same as dueling, disallows the use of a shield, but allows a stronger AC bump via reaction. This scales pretty strongly too, eventually increasing AC by more than the Shield spell without the spell slot cost, though only for a single attack. Scaling AC bumps this way is overpowered with bounded accuracy.

The feat is on par with PAM and GWM probably, but may be introducing some power creep. The BA attack is stronger than PAM and more reliable than GWM. The to hit penalty is more forgiving than GWM/sharpshooter, and damage would probably be comparable in cases where you'd use it. The reach bit seems strong, especially if built for.

I think the bigger issue is that they're too similar to existing options. The disallowing of using a shield makes it effectively 2 handed use only.

Perhaps a better approach would be to lean into versatile. Have the fighting style allow you to use the higher die one handed, and maybe a +2 to hit when used 2 handed making it not quite as good as dueling when using a shield, and more accurate at the cost of defense.

Answer 3

At least the fighting style is certainly overpowered

• It confers basically the benefit of the Defensive Duelist feat (with the minor difference of holding a versatile instead of a finesse weapon) but does not require 13+ Dexterity to work. The feat itself is not overpowered, still this bonus seems to be powerful.
• It has an additional benefit similar to the benefit of the Dueling fighting style. If, as it was pointed in @stevenjackson121's response, this is a flat +2 damage from all sources, then it is even stronger. Even if we read the +2 damage being added only to the attacks with the versatile weapon, it is still only slightly weaker then the Dueling variant.

A fighting style giving both a close eqiuvalent of another fighting style plus an okay feat on top is much stronger than the average.