Help, I'm a DM

Probably not all 5e combat is like this. But, like, look at the statblock for the Tarrasque, the CR 30 "strongest monster in the game" and try to tell me that that thing looks INTERESTING to fight. Difficult? Maybe, if your stats are bad. But INTERESTING? It walks at someone and murders the shit out of them, then rinses and repeats. The fetid dog turd that is the Tarraque is the perfect example of the Bigger Number, and even its meme status as the DM's "fuck you" monster is eclipsed by later additions to the game.

The other end of the "strongest 5e statblock" spectrum is shit like Sul Khatesh from Eberron, who earns the title of "most bullshit" by being immune to nonmagic attacks and creating antimagic fields. This is progress, because you might force someone to grapple it out of the field or something so everyone can deal damage! But this is still ultimately a pretty linear fight, not unlike fighting any other caster in the game, but with Less Counterplay.

My DMing style is pretty character goal-oriented, with the occasional bullshit superboss. We sit around for a few sessions while people pursue side projects and gather information, and then I subject them to the Horrors of a 5e fight that requires things like "positioning" and "planning" from turn to turn.

When playing a high level D&D campaign with insanely bullshit homebrew magic items and character-specific custom mechanics, it becomes necessary to pull out the big guns. The biggest guns. I'm talking a gun like my boy Hierarch Ozyas, undead demigod, father of monsters and heart of a living city, who had a meaty 2000 hit points and took somewhere in the vicinity of thirteen rounds of combat to bring down. Building bosses is an arms race and it's my job to lose in style. Here's Ozyas' statblock:

The bitch himself

Anyways I've been talking for a bit without actually saying anything of substance besides making fun of the Tarrasque. Which I will do one more time:

...deep breath...

D&D 5e is a pretty widely-disdained game by pretty much anyone who's ever played more than one RPG system. I myself only play it because I enjoy game design, and the thoroughly-beaten dead horse that WOTC calls a game serves as a decent foundation to do a lot of heavy tinkering. The Tarrasque is perfectly emblematic of all of the trash I have to wade through in order to get to the stuff worth keeping: it is an uninspired, anticlimactic relic of the past that didn't even manage to cling to a shred of its old glory and is instead content to wallow in the filth of what it once was, never once providing a challenge to any character with a flying speed. I would probably attempt to beat it to death with my hands (and fail, because it checks your character's stats rather than challenging you as a player in any way), but Jim the 1st level aaracokra with a save-forcing damage cantrip already solo'd it for me, so I'll settle for chewing through the throat of whichever game designer forgot they were making a "game" and submitted a three step flowchart for D&D's ultimate boss monster.

But anyways, I promised you a guide to how I design boss fights these days, so let's get to that.

Actually, first here's a quick aside about action economy that I didn't bother finding a place to fit in elsewhere: legendary actions are basically a necessity for any boss past level five or so. One big action is going to be a lot more polarizing than several small ones (i.e. one big crit on a large attack could completely flip the course of the fight, whereas multiple smaller attacks offer the same amount of damage output in a more consistent fashion). If you don't want to give your boss a bunch of HP to make it live long enough to take a few turns, you could consider giving it two turns in the initiative order (reducing the damage per turn to keep the damage per round constant). Low health minions are also a good way to pad out action economy, and even if they're easy to kill they tend to buy the boss another turn or two just from the actions it costs to take them down.

ANYWAYS, here's the core ideas I like to focus on in my boss design:

Keep them moving

Keep them working

Keep things changing

Reward good play

Punish mistakes

Make it a game

Along the way I'll be using snippets of the boss I mentioned above to illustrate examples of these principles and how they affected play. Let's begin.

KEEP THEM MOVING Positioning doesn't really matter in 5e. AoEs and movement values are both so large that you can easily get away with not having a battle map and sorta just tracking "in melee" or "not in melee." I run most fights without a battle map and just kinda track that, but for a good boss you need a map.

But how do we keep the game from just falling back into "move into range and hurt people," you ask? Simple: the Zone of Nasty. The Zone of Nasty is something on the map that is going to hurt the PCs if they're in it, and the Zone of Nasty moves. Depending on the boss, it could grow, shrink, follow a player, follow the boss, alternate between areas of the map, whatever. Some bosses might have multiple different Zones of Nasty that move in different ways and do different things.

There are other ways to force movement besides a moving AoE, such as punishing players for being too close or too far from each other or the boss.

The general principle here is that a boss should at times force suboptimal play: optimal play involves simply standing around, spending all your actions on damaging the boss, and it's incredibly boring from a strategic standpoint. There should be turns in which your players have to spend their action economy on protecting themselves or helping their allies. If they find themselves in a Zone of Nasty, it should force a decision between suffering the consequences to continue optimal play, or spending resources to get out of it.

Our boy Ozyas had a Cancer Field that he could move slowly around the arena that damaged and debuffed PCs inside it, and Pretender-God-Piercing Strike, a telegraphed line attack that oneshot anything that stayed in its area too long (more on this one later).

KEEP THEM WORKING Everyone needs a job to do! This job is probably just going to be based on what their class and abilities encourage them to do, but it sucks for someone to not be able to meaningfully participate in a boss fight.

Let the DPS players kick the boss's teeth in, obviously, but make sure the person who focused on AoE effects has some extra enemies that they can deal with. Bonus points if the extra enemies have something that forces them to be dealt with instead of just rushing the boss' HP bar.

Worst case scenario, throw in a secondary objective like completing a ritual, controlling a point on the map, or fighting the boss' soul on a higher plane to give someone who isn't immediately needed for DPS to still have something to do.

Ozyas spawned a bunch of extra monsters from these gross Birthing Pillars around the map, and killing the monsters and destroying the pillars provided a nice secondary course of action for people either not equipped to slug it out with the boss or not currently positioned right to fight him.

KEEP THINGS CHANGING The tarrasque sucks because it does one thing over and over until it works or it dies. The Theros splatbook improved on this marginally: Mythic Traits are fucking baller! Combats should change over the course of the fight, or this could have been a fucking autobattler. But we can go further.

In addition to occasionally shaking things up based on health thresholds, here's a few ways I like to do it:

Rotating list of effects that change every round

Huge list of options the boss can choose from for one of their effects with no repeats

Some sort of meter that increases and decreases based on what's happening in the fight and modifies the boss' abilities

Ozyas summoned new monsters every round and could customize the statblocks with a bunch of quick templates I whipped together, and in his second phase he started alternating between scaling the to hit/damage of his tentacle attack, the reach of his spear attack, and applying extra buffs to his summons.

REWARD GOOD PLAY These next two kind of tie together but the core idea here is that it's okay if a boss is a bit easy, as long as it makes your players work for it.

This can include things like ways to trivialize certain parts of the encounter as long as the players utilize them, typically at the cost of advancing other parts of the fight.

I knew that Ozyas was going to be a long fight, so I gave my players the ability to heal to full health, as an action, whenever they wanted. They were fighting inside Ozyas' body, and he was a generous host. However, any time they healed, he would be healed for the same amount. They got around this restriction by hitting him with Chill Touch to disable his own healing whenever people needed to heal, but that obviously had the cost of losing two actions' worth of damage output.

Towards the end of the fight, everyone was still standing thanks to that healing, but as he began to infinitely scale his stats once he reached his second phase and started taking them seriously, they couldn't afford to waste turns healing anymore and the safety net they built up by healing earlier in the fight kept anyone in the party from dying.

PUNISH MISTAKES The range on D&D characters' HP pools and general survivability can be pretty broad. I like to give my bosses a reasonably-heavy hitting melee and some sort of light ranged attack to remind the backliners that they too can die. But there's a third kind of attack.

The great equalizer.

The One Hit Knock Out move.

These need to be telegraphed. There needs to be copious time to get out of the area, or to stop the boss from using it, or whatever the case may be. But any superboss should have a way to threaten any player on equal standing: a move that will always hit if its conditions are met, and puts them clean to 0.

Ozyas' OHKO was Pretender-God-Piercing Strike, where at the end of each turn he would wind up a spear thrust with enough range to hit across the entire map, targeting a 15-foot line through the nearest player. Neither he nor the line could move after that, and if you were still in that line at the start of his next turn, you were done.

It wasn't hard to avoid: just walk like 10 feet and don't get pushed back in by another enemy. They even lined it up to target some of his own allies sometimes. But it forced them to think about positioning and stay moving, and there were a few times where it aaaaalmost caught someone in the line. The prospect of Instant Death really does wonders to ratchet up the tension.

And now, finally, we come to the most important part:

MAKE IT A GAME D&D 5e likes to jerk off while fantasizing about being real. "Catherine what the fuck are you talking about?" What I mean to say is that D&D makes a fumbling attempt towards a more simulationist style of game, trying to distance itself from the fact that it is, in fact, a game. It tries to comport itself like reality, such that every part of its combat makes sense in-universe, and then immediately falls short because it can't be assed to indulge in actual simulationism.

It is my belief that if you're going to spend 4 hours fighting a boss, and one of the boss mechanics doesn't really make much sense as an in-universe concept but does make the boss more interesting and fun to fight, then that's a perfectly fine mechanic. Obviously finding some way to justify it is preferable, but my bosses prioritize good gameplay over verisimilitude.

The upcoming boss in my campaign has a feature which puts the fight on a ten-round time limit before he begins kicking substantially more ass than he was before (and the prior ass-kickery was indeed already substantial). If this is a desperate fight with his life and his dreams on the line, why doesn't he open with that? If this were a WOTC statblock, barring a mythic trait, that's exactly how it would work. But fuck that, because it would make the fight way less interesting! Now there's time pressure! And sure, the post-round-ten version of the boss is meant to be fled from, not fought, but if he's at a low enough HP it could instead make for an insane climactic finish!

I let my players see the whole statblock before the fight. We talk through all of its abilities, and I'll even point out some of the potential points of complexity and the big risks to watch out for. There's no in-universe justification for why the characters would know this (beyond, perhaps "you're exceptional adventurers and are good at evaluating your foes"): in fact, one of the quintessential examples of classical 5e metagaming is the Guy Who's Read the Monster Manual. I think that's fucking stupid, though. With open statblocks:

Features can be game-warpingly deadly without instantly incurring a TPK born of ignorance. OHKO moves don't feel fair unless the counterplay is known

The players can strategize around the ways in which the boss is going to change throughout the fight

It's fundamentally fair. Some GMs just wait X turns and then let the boss go down when it takes a big, impressive hit (and I fully respect people who do that! That's still more compelling boss design than 5e's normal schlock), but I personally like when numbers have meanings.

You can still hide some information (I like to black out the boss' Mythic Trait, and then only use it if the players stomp the fight too easily), and you can still tweak it to adjust the difficulty, with the difference being that your players know it's being adjusted and how so (which again comes back to my feelings of fairness).

A few other fun mechanics to toss in include stacking debuffs that trigger something horrible at some certain threshold, additional win conditions or lose conditions, and silly little minigames. One trick I particularly enjoy is having my players secretly vote between two or more bad outcomes, and punishing them even more if the vote is tied.

CONCLUSION Your mileage may vary, but I'm hoping at least some of the insights here were useful to you! I have a particular strain of undiagnosed mental illnesses that make me especially predisposed towards piloting huge convoluted intricate bosses with 1k+ word statblocks, and I'm lucky enough to have players who know their shit well enough to play around this bullshit. Find something that works for you and your players.

If you hate 5e combat and think this sounds like way too much work to be worth doing, go play something else, like Pathfinder or Lancer or (heaven forbid) a game that actually struggles to trace its lineage of inspiration back to D&D. Go to itch.io and find some game no one's ever played before, and toss the creator a bit of money. The only way we're making it out of these goddamn Mines of Phandelver is if people try something new from time to time.

On the subject of cool games with cool combat, bear with me as I shill for a friend real quick. If you want a game that cares less about combat as an abstract dick measuring contest and more about combat as a facet of violence and all that that entails, check out [BXLLET> by @rathayibacter.