Is this Monkey Grip port balanced as a 5e feat?

Question

There is a feat in D&D 3.5e called Monkey Grip. I am considering this 5e feat inspired by that:

Monkey Grip

Wielding a weapon made for a creature one size larger than you doesn’t impose disadvantage on your attacks.

This means, assuming you are Medium and you wield a Large weapon, the base damage die of the weapon is doubled. At best—a Large greatsword or maul—this adds +2d6 damage, or on average +7, to each attack.

Great Weapon Master offers +10 damage at a −5 attack penalty—but you can also choose not to use it if you need the accuracy, and Great Weapon Master also offers the option for a bonus-action attack on a crit or kill. I strongly suspect that a +3 relative bonus in damage is not (remotely) worth a −5 penalty to attack, and I have doubts that the bonus-action attack, as limited as its triggers are, is going to make up the difference. Is this version of Monkey Grip clearly superior to Great Weapon Master? Is there any case in which Great Weapon Mastery would be the optimal choice when this Monkey Grip is available?

The comparison with Sharpshooter, it seems to me, is a little better—the same −5 attack for +10 damage, but the other effects of Sharpshooter seem far more valuable. How does that stack up?

The other consideration is that Monkey Grip and Great Weapon Master could be combined, for a possible +17 damage—unprecedented so far as I know, since most of the direct combat feats are incompatible with one another, unless there’s some way to make a “melee attack” with a “ranged weapon” in order to qualify for both Great Weapon Mastery and Sharpshooter. Still, we could just add a clause to Monkey Grip barring it from being used in combination with Great Weapon Mastery, if necessary, as I suspect it is.

The 3.5e Monkey Grip feat came with a −2 penalty to attack rolls. In that system, that penalty was not worth the benefit, but the benefit was only +1 damage, on average, not up to +7 (unless you really worked at it, but that took much more than just picking the right type of weapon). And, of course, 3.5e math and 5e math are quite different. So I have, for the initial version of the feat, left that out—but the comparison to Great Weapon Mastery leads me to suspect that Monkey Grip needs something. Is a −2 penalty the answer? Comparing Great Weapon Mastery and Monkey Grip, you’d be looking at a −3 relative attack penalty for a +3 relative damage bonus—is that better-balanced? Does it expand the situations in which Great Weapon Mastery is the optimal choice? Does it leave other cases where Monkey Grip is the optimal choice?

Most 5e feats do more than one thing, too. Great Weapon Mastery has the bonus-action attack, Sharpshooter mitigates the difficulties of long range and/or cover. Monkey Grip should probably have something too—I’m kind of leaning towards an Intimidate-based effect, since the whole concept of Monkey Grip is the badass image of someone with a huge freakin’ sword—be nice to see that image have mechanical effect. But I have left that out, too, on the basis that Monkey Grip already looks too good compared to Great Weapon Mastery and GWM’s bonus-action attack or Sharpshooter’s range/cover mitigation might make up the difference. So it would be nice if answers also addressed how large a consideration the bonus-action attack or range/cover mitigation is in determining whether or not Monkey Grip is balanced—if, for example, the lack of an add-on feature makes the difference between the −2 penalty being “enough” for balance, I would want to know that.

Answer 1

A big issue you will have is when people start trying to use ranged weapons with the feat, crossbows that deal 2d10 +pr +dex. Now combine that with crossbow expert and you start dealing 60+damage per round from 100ft away while spell casters need to use a limited resource to achieve this. Now take sharpshooter as well. Great Weapon Master explicitly limits you to melee weapons. At the very least you should limit Monkey Grip to melee weapons.

The other issue is when they start combining this feat with others, like Great Weapon Master, a PC can start approaching massive damage rules and it starts making other players less relevant in combat. I think you are underselling Great Weapon Master; with the damage increase, multiple attacks, and class abilities getting a crit or killing an enemy per turn is not hard, so dealing an extra 30+ points of damage per turn is not uncommon (+10 plus another attack with +10). Great Weapon Master is easily the better choice, but when you start adding things that can easily stack with Great Weapon Master you start breaking 5e combat. Getting advantage is not hard in 5e. There is a reason there are multiple questions about balancing Great Weapon Master.

Honestly your best bet might be to just reword Great Weapon Master, and just say they are using really big weapons; the size of a weapon is mostly flavor anyway.

By using oversized weapons you can increase the power of your strikes

You gain the following benefits:

When you make a melee attack with such a weapon with which you are proficient, you take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attack’s damage.

On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.

If the interpretation of proficiency worries you, just say it also grants proficiency with oversized weapons. Weapons are not that granular so you could also easily justify a oversized greatsword as still a greatsword, just with its own quirks.

You could just also just use Great Weapon Master as is and just say it manifests as you using huge version of the weapons. Make it pure flavor.

Both give them more damage with a penalty much like the original monkey grip feat and prevent stacking (since it is replacing great weapon master). It also feels more like a character wielding a huge weapon, dealing lots of damage and cutting through multiple people with the downside of it being a harder to use. I really think this is why they did not include monkey grip as a feat as it is, being duplicated fairly easily with Great Weapon Master and some flavor.