When the new Player's Handbook came out about a year and a half ago, I think the class that got the biggest glow-up was the Monk - many of its issues were solved, and in many cases the class was simply empowered. That being said, I've also seen a number of theory-crafters argue that, while improved, it's still around the bottom rung of the class power.
Now, one thing I think these optimizers often ignore is defensive capabilities: by changing Deflect Missiles to simply Deflect Attacks, the Monk now has one of the most powerful defensive abilities in the game, probably only second to the Barbarian's rage (even with significantly lower AC than a Fighter or Paladin in full plate with a shield, I found that a Monk wound up taking less damage even from a Marilith, whose many attacks per action dilute the single-attack damage reduction of the Monk's Deflect Attacks).
However, this series has focused on damage output, and so we shall continue to.
The Warrior of Elements is, ostensibly, the update to the Way of Four Elements subclass from 2014, but in truth, it's a totally different subclass, merely replacing the old one by sharing its elemental theme while rebuilding everything from the ground up in terms of mechanics.
The subclass is built around Elemental Attunement, which you can activate to grant you various benefits, not the least of which is that your attacks gain a much longer reach.
Now, there's a weird nuance here, and I don't know if there's been any official ruling on it, but the reach affects all of your Unarmed Strikes, which now includes both grappling and shoving a target.
If we then assume that this reach is not in any way interrupted by, well, just not being currently in the act of attacking, it should allow us to grapple targets up to 15 feet away from us, which could be a huge defensive boon, as it could effectively shut down a foe that doesn't have ranged attacks.
Assuming this interpretation is correct - that we could hold a foe and continue to strike at them while they can't hit back - we can build a character around grappling.
Notably, this might not be amazing against our boss monster, the Death Knight, because they are A: very strong and B: have legendary resistances. Still, it'd be a decent gameplan for a whole campaign, and could still wind up having an effect on the boss fight. Let's get into the build:
Feats:
I always run into this problem: I know that feats are powerful enough that it's often fine to leave a score uncapped in favor of getting the functionality of a feat. But it bugs my OCD tendencies. And Monks, in particular, really want high Dex, high Wisdom, and high Stamina.
Now, the thing with Monks, though, is that a lot of martial feats don't really do anything for us. Great Weapon Master doesn't work with any Simple weapons, and Polearm Master's biggest boon, the Pole Strike attack, is kind of redundant with our martial arts. We don't natively get Weapon Masteries, so Dual Wielder isn't really going to help us. Crusher can be ok for us, but we already get the ability to push targets with our elemental strikes.
But Grappler is pretty great: as Monks, we can use our Dexterity to set the DCs for our grappling attempts, and we're already making plenty of Unarmed Strikes anyway. Finally, the Fast Wrestler aspect of the feat lets us drag grappled targets quite far given how fast we move (and with Slow Fall, we can even drag foes off of ledges to potentially give them fall damage while we can just absorb it).
So, we'll assume we get 17 Dex at level 1 and then bump it to 18 with Grappler at 4. And then... I think we just cap it with an ASI at level 8.
It's probably "optimal" to just take 15s in Con and Wisdom at level 1 as well and dump the other three stats, though I never really like to do that (I hate having more than one negative modifier). Instead, I'll assume we do try to get Wisdom up to 16 at the start, and have at least a 14 in Con, but we might not have utter garbage scores otherwise.
I've generally avoided talking about origin feats here - Tavern Brawler actually has a lot of redundancy with being a Monk, but it does still boost our damage a little, letting us reroll 1s. This gives d6s an average roll of 3.9ish, a d8 an average of 4.9ish, a d10 an average of 5.95, and a d12 an average of 6.96ish, so essentially giving you .4 damage per hit, and thus, with a level 10 Flurry of Blows, about 2 damage overall if everything hits. It's not nothing, but it's not huge either.
Still, the Sailor background will cover you for this feat and your preferred ability scores. I'm not going to take Tavern Brawler into account for my calculations - grabbing Tough or Alert, Lucky, what-have-you, might be more ideal depending on your campaign.
Grappling a Death Knight:
Now, the big thing: grappling in 5.5 has the target make a saving throw - their choice of Strength or Dexterity. Normally, this is set by your Strength modifier, but Monks have special dispensation to instead base it on their Dexterity (I think there's a world in which Monks should be a Strength-based class, but overall they're probably better-off being Dex-based. I need to take a look at the Pugilist class).
At level 10, we should have a Dex of 20, which means that the saving throw DC for our grapples will be 17.
Now, a Death Knight is strong, but like Paladins, they don't actually have proficiency in Strength saving throws. Thus, they merely add their Strength to the roll. Also, while they have Magic Resistance and they also have Marshal Undead, they are explicitly not personally affected by the latter feature (which grants other undead creatures of the Death Knight's choice within 60 feet of themselves advantage on attack rolls and saving throws).
Thus, the Death Knight is actually more likely than not going to fail the save against our attempts to grapple them. On a roll of an 11 or lower, they fail, meaning we have a 55% chance to grapple them.
That's actually great news. But I also don't think that means it's likely we actually will grapple them: this is something the Death Knight will probably use their legendary resistances to get out of.
Because we have the grappler feat, there's no actual cost to trying to grapple them once per turn, and we reap a great reward if we succeed - we get advantage on our attacks against them (which is pretty great given how high a Death Knight's AC is.)
So, how do we account for this?
Well, I think I'm going to go the simplest route: the DK is always going to LR out of being grappled by us - while they do have some ranged options, like Hellfire Orb, the Fell Word legendary action, or their spells, being grappled by us and allowing us to just pelt them with elemental strikes from afar is just not acceptable.
But that's great, because if we can burn through their legendary resistances, it opens up our allies to get them with various spells and such that might be even worse for them.
Gameplan:
We're assuming this is a major boss and we're pulling out all the stops, and that means using Flurry of Blows every turn. I think we're also going to be using our action to attack, but I will check the average damage of Elemental Burst to ensure that that's actually correct. Still, we'll be burning a Focus Point each turn to get what are now three additional attacks as a bonus action (once we hit level 10, which we are).
At this level, unless we have a magic weapon, our unarmed strikes will hit just as hard as a spear or quarterstaff or greatclub anyway, and we get the extra range for them from Elemental Attunement, so we'll just stick to them. (Also, DMs, if you're handing out magic items, give the Monk some Wraps of Unarmed Prowess. Honestly, I'd have liked to see Very Rare wraps that add damage dice as well, like a Vicious Weapon).
We have 10 Focus Points at this level. We need to spend 1 to get Elemental Attunement going, but then we have 9 left to spend on other features. We're assuming one each turn for Flurry of Blows. Our Focus saving throw - which is based on Wisdom - is only 15 at this level, but that does mean that a Death Knight has to land a 10 or higher to save against Stunning Strike, as they only have a +5 to Con saves.
Thus, I think it's actually worth it for us to spend a point on Stunning Strike each turn as well (assuming we hit) to burn through Legendary Resistances that much quicker. If we can land a grapple and a stun on turn 1, we could burn through all 3 LRs on turn 2 (though we'd have to be fairly lucky. Given that we're making 5 attacks per turn - assuming we aren't Elemental Bursting - there's a strong chance we'll land at least one attack per turn, but there's only about a half chance that the DK fails the save on any of these).
Thus, we're spending 3 FP our first turn and then 2 more for each subsequent turn, meaning we can sustain this for four turns, which is actually pretty good - few combats go longer than that. Now, we might need to use FP on other things - naturally if we get into a situation where we need to do something like Patient Defense or Step of the Wind, this "blank room" simulation no longer really applies.
Damage Per Attack:
All of our attacks do the same damage and have the same hit chance, so this will be a pretty simple thing to calculate: We have a +9 to hit at this level, so we hit 50% of the time. Our attacks do 1d8+5 damage, or 9.5 on average, with an additional 4.5 damage on a crit. Thus:
50%x9.5 is 4.75 and then 5%x4.5 is .225, so we're looking at 4.975 damage per attack.
If we were to just leave it at that, with 5 attacks, that's a total of 24.875 damage.
That's not terribly impressive, but let's consider some other options.
Elemental Bursting:
Because our various bonus action attacks are no longer tied to having to first take the Attack Action, we can actually replace our attacks with Elemental Burst. This costs 2 Focus Points, but lets us drop a Fireball-sized sphere of elemental energy that does, well, a Shatter's worth of damage. It deals, at level 10, 3d8 damage (we'll say Thunder as a default as that's pretty reliable, though all should work on a Death Knight). On a successful save, creatures take half damage.
Now, our Focus save DC is only 15. A Death Knight has a +6 to Dex saves (they get proficiency in Dex saves rather than Charisma, compared to a Paladin) but on top of that, they have Magic Resistance, so they'll have advantage on this save.
Thus, if they succeed on a 9 or higher and have advantage, we're looking at only a 40% chance squared, or 16% chance to actually fail the saving throw.
On a failure, they take 3d8, or 13.5 average damage, but they still take half, or 6.75 damage on a success.
Thus, this will do 13.5x16%, or 2.16 plus 6.75x84%, or 5.67, giving us a total damage of 7.83. Not only are we spending 2 FP on this, but we're also sacrificing our two regular attacks, which each do 4.975 damage on average, meaning we're about 2 damage behind.
Yeah, Elemental Burst is not bad for big groups of foes, but it's not worth it in this case for a single-target encounter.
Burning Through Legendary Resistances:
Now, we need to talk about the nuance of advantage. In an ideal world, we can grapple the Death Knight, or stun them, and thus get advantage on our attacks against them.
Now, there's an interesting nuance at play here: a stunned target automatically fails Strength and Dexterity saving throws. While Stunning Strike is not as powerful as it used to be because it ends before our next turn (and we can only use it once per turn,) we can still use it both to give our subsequent attacks on our turn advantage as well as to automatically get our grapple off. However, we also do automatically get advantage on our next attack even if they succeed on their save, so there's some utility to trying it even if we can't get a failed save. The stun is somewhat ephemeral - it only lasts until the start of our next turn (though that's fantastic for our allies) but if we can stun them, we should then be able to automatically grapple them, and they'll notably not have an action on their next turn to break the grapple, so we will have advantage on our attacks thanks to the Grappler feat.
Stunning Strike is maybe the number one thing that a Death Knight would spend Legendary Resistances on.
So, how quickly can we burn through them?
Again, our Grapple DC is 17 while our Stunning Strike DC is 15. We'll assume we're burning both every turn. Both require us to land an attack on the target. With 5 attacks every turn and a 50% chance to miss, we have around a 97% chance to hit with at least one attack each turn, so I think we're talking really extraordinary bad luck if we don't.
If we have the opportunity to make a Stunning Strike, the Death Knight will make the save on a roll of 10 or higher - a 55% chance to succeed.
Against our one free grapple attempt per turn, the DC is higher, though they can choose to make a Dex save instead, which is actually higher for them. With a +6 against our DC of 17, they succeed on an 11 or higher, so a 50% chance.
So... what if we did something else?
What if we sacrificed our own damage to try to lock down this Death Knight on our first turn?
If we chose to, rather than attack, just try to grapple over and over on our first turn, how likely is it that they'd fail their saves?
(I'll concede here that as someone who hasn't taken a math class in about 21 years, I'm not sure if I have the tools to figure this out).
Now, we do need to land an attack to try Stunning Strike, and we also get a free grapple attempt if we hit with an unarmed strike, but only if we hit.
Ok, screw it, let's say that we just want to try to grapple the Death Knight at least to start with - to lock them down as soon as we can. In this case, we're going to make 5 grapple attempts.
With a 50% chance to fail or succeed, the chance that they don't fail on at least one of those attempts is a little over 3%. Thus, it's a little less than 97% that the Death Knight has to burn a legendary resistance.
But how likely is it that we can burn through all 3 on turn one?
Again, my early-2000s high school math skills are very fuzzy in the back of my memory, but let me imagine how to approach this:
With 5 attacks, we figure that there's a 97% chance that we get at least one failure. But if we set that failure aside, we now have 4 attacks that we'll need to have at least one failure in. Over four attacks, we've got a 93.75% chance for one to fail. Then, if we had those two failures, there are three remaining attacks on that turn, so there's an 87.5% chance that there was one failure among those.
So... uh... What does that actually tell us?
Ok, I think I've got it:
Basically, we have a 97% chance to burn through one LR. Within that 97% chance, there's a 94% chance (we're going to round) that we burn another one, so that's about a 91% chance. Then, within that 91% chance to burn two legendary resistances, we have an 87.5% chance to burn one on the other three attempts, giving us around an 80% chance to burn three.
That doesn't seem right, does it? Is the flaw here that we're accounting for the earlier saving throws multiple times? Given that we need a majority of the saving throws to fail, I'd assume that with even odds, that'd be less likely to happen than not. Or is this just a place where intuition is misleading me?
Again, let me think about this:
We figured out the chance for any one of the saving throws in a set of 5 is to fail was 97%, because every single one failing would be 50% to the fifth power, which is about 3%.
Is the next move to multiply that by the chance that we get a failure on the four remaining dice?
Ah, this is driving me nuts and it's late at night. I'm sure someone who understands basic statistics would figure this out for me in moments. But, let's just figure out one more thing:
Damage with Advantage:
There are a lot of ways to get advantage on our attacks in 5.5, and while we don't have the Vex property to work with, if we do succeed in grappling and/or stunning the Death Knight, how will that affect our damage output?
Well, thankfully, with a clean 50% hit chance, it's pretty easy to figure out what our hit chance is with advantage: 75% to hit, and the usual 9.75% to crit. Once again, our hit damage is 1d8+5, or 9.5, and our extra d8 of damage on a crit is 4.5. So, 9.5x75% is 7.125 and 4.5x9.75% is .43875, so our average damage per attack when we have advantage is roughly 7.6.
Thus, if and when we do get advantage on all our attacks, our damage jumps up to 37.8 per turn, which is a pretty enormous jump, and I think pretty respectable.
I'm sort of giving up on how long it will take us to burn through a Death Knight's legendary resistances to accomplish this state. (I really don't feel like there's an 80% chance we get 3 failures on turn one, but I can't figure out where the logic in my math falls apart.) But not only will it greatly benefit us, it will also potentially really help protect our party. Other combatants won't get the advantage we gain from grappling the target, sure, but we can ensure the Death Knight isn't able to attack the squishier members of the party, and we can drag them through dangerous terrain (I will say, there's a bit of a rules blind spot when it comes to dragging a foe around us rather than just pulling them after us) - like pulling the Death Knight through a Spike Growth or something of the sort.