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D&D 5E The Hardest Encounters


As you work your way through GMing a campaign, you add more and more complexity to your encounter design. Venomous critters appear. The orc shaman starts casting spells. Lair actions crop up when you finally meet that baby dragon at the end of the baby dungeon. It’s all cumulative, and it’s all meant to help prepare you for the actual end-boss of GMing: running high-level combat.

So here's my question to the board: What’s the most mechanically complex encounter you’ve run? Were you its equal, or did you find yourself overwhelmed by all the rules and options? Any way to combat getting bogged down in complexity?

(Comic for illustrative purposes.)

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Magic Wordsmith
It's not particularly complex per se, but when the DM sets up an encounter that is going to involve monsterbating (i.e. having monsters attack other monsters), it's best to think about how to abstract that out of the normal combat rules so as to avoid a lot of DM-on-DM action that takes away time from the players.

I have otherwise not found high-level play to be complex enough to slow things down even with some of the elaborate set pieces that I'm known to create. The only thing that bogs it down is if the players aren't very familiar with their characters, which is why I don't tend to run high-level one-shots.

I once ran an encounter that took place in a winding canyon against a dao, efreeti, and some elemental minions. This was their third encounter of the day against two CR 11's and a few CR 2s. I don't remember the player's levels but it was a deadly encounter whereas the other two encounters were in the medium to hard range. It was already going to be a lot to track but I designed the map to allow for earth gliding in most places. The only places that were "safe" were the stream and on top of a couple vehicles that the players were trying to take. The efreeti used its fire wall ability to block off the vehicles while throwing flames at anyone that approached. At one point the dao's minions were pushing boulders into the canyon. I didn't even use the dao or efreeti's fly abilities because it was already enough to track everything else on top of the PC shenanigans.

I felt up to the task and it was a pretty fun encounter. I wish I could go back and run it again knowing what I know now. I'm confident I could make it a bit more streamlined.

The show must go on. DMs should never stop to think longer than max. 30 seconds per turn during combat. So, no complexity for me, even at high level.

But I don't consider legendary actions or lair actions particularly complex. And some damage resistance is also not very complicated. The real complicated one is spellcasters with lots of spells at their disposal. As a DM I usually don't know their spell-list by heart, so I need time to play it optimally. That will slow down a game, which I don't allow myself to do... i.e. my answer to the OP's question: I get overwhelmed with too many spellcasters when they all have different spells at their disposal.


It was the party versus 100 githyanki, 3 battleships, 10 gith warriors, and a gith battle captain.

I made an excel to handle all of the rolling for saves and attacks


The most complicated encounters I've run are in 3D, usually underwater. For whatever reason, it's very hard for some players to wrap their mind around it. I think going theater of the mind would be better, as every time I've tried to use minis, it seems to make it worse.


The most frustrated I have ever been running a 5E encounter has always been against a singular big bad. Not because they are complicated, but because they suck. Luckily I eventually learned to redesign "solos" in a way that makes them viable.


My 6 players were teleported into a Village, that was attacked by an army of undead. So I had my 6 party members, like 6 fighting Villagers who manned the walls, 1000 Zombies and Skeletons, 2 Zombie T-Rex, a skeletal dragon and two homebrewed pseudolichs as the commanders. The players were level 4 or 5 and won by taking out the liches. They were actually only supposed to hold out long enough for reinforcements to arrive. But they did it ... ah yes, in the middle of the fight a small goblin troop on real T-Rexes arrived (helping the players). That was fun but also an exhausting 7 hours of game day.


I will say in general the most complicated combats involve a lot of types of creatures. Like an ensemble of 6 different monsters is much harder to run than 20 of the same type. This is doubly compounded with spellcasters. 1 spellcaster is always a pain, 2 spellcasters is more than double trying to keep straight who has what spell.

I will also note that creatures with reaction are like 2x-3x more complex than cretures without them, its so damn easy to forget about those reactions!

My vote would be either the final battle of Rime of the Frostmaiden or a recent large-scale battle I ran that had multiple regions with different challenges, plus random battlefield events.

Was I their equal? I like to think so, but certainly with the former, which spanned three sessions, I had to take copious and detailed notes.

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