D&D 5E Level 20 Dragon Fight design advice

[Reynard]

I want to run a one shot of a party of 5 20th level PCs versus a powerful dragon in its lair. While I have been running (and designing for) 5E for all of its life, I have never run 20th level before.

A few context notes:

PCs will be custom built for the fight, with access to PHB, Xanathar's and Tashas.
It will be one shot without a lot of story, focused on the tactical experience.
It will be played on Fantasy grounds, using a grid, line of sight, etc.

The experience I am going for is very difficult but fair, and fun.

My biggest concern is action economy. I am thinking of combining minions with terrain to make sure the PCs can't just gang up on the dragon.

Thanks for your help.

 

[RoughCoronet0]

If it’s possible, you could look at Fizban’s and take inspiration from the greatwyrm, Bahamut, and Tiamat stat blocks to design your dragon. I would definitely give the dragon access to various minions, terrain effects depending on the dragon type, abilities that strengthen its defenses, a few magic items, as well as giving it a short list of spells that it can use to change things up if necessary.

Also remember that dragons that are powerful enough to be a threat to level 20 PCs are typically very intelligent and have had thousands of years of experience dealing with all manner of adventures. So they will not act like simple brutes that storm into the middle of the fray without a great deal of contingencies in place.

 

[nevin]

I want to run a one shot of a party of 5 20th level PCs versus a powerful dragon in its lair. While I have been running (and designing for) 5E for all of its life, I have never run 20th level before.

A few context notes:

PCs will be custom built for the fight, with access to PHB, Xanathar's and Tashas.
It will be one shot without a lot of story, focused on the tactical experience.
It will be played on Fantasy grounds, using a grid, line of sight, etc.

The experience I am going for is very difficult but fair, and fun.

My biggest concern is action economy. I am thinking of combining minions with terrain to make sure the PCs can't just gang up on the dragon.

Thanks for your help.

first of all the only way to prevent the characters from Ganging up on the Dragon is to make them fight it outside. Secondly there is no fair at 20th level any success or failure can change the flow of the game at a moment. At 20th level if the Dragon is smart it would come in at dusk, on a foggy morning etc and make a dive attack on the party eating breakfast and try to catch them by surprise and kill the mage and or cleric with breath weapon. Then fly away and adjust tactics from there. If party comes into their lair if the dragon has fire the lair should be in a tar seep, have the floor covered with sawdust, flour or other flammables that can easily be thrown into the air with wing buffet and when they are thrown in the air you get breath weapon that explodes dust in the air causes 20d fire ball along with breath. If dragon is really smart cave in the entrance first then burn up the oxygen. Or better green dragon in low oxygen cave filling cave up with poison gas. At 20th level if they dragon knows they are coming, or they are stupid enough to crawl into the cave it should be a miracle if the entire party survives. Dragons are long lived smart charging in and fighting should be the last thing it would do and I'd expect the cave to have some back door that requires part to be able to fly to follow or swim in a really fast powerful underground river, hot toxic lava tube etc.

 

[Reynard]

first of all the only way to prevent the characters from Ganging up on the Dragon is to make them fight it outside.

Thanks for the reply, but I wanted to quibble with this a little bit. I don't think it is true at all, to be honest. Lair terrain can serve to channel and separate players pretty easily. Even 20th level characters can't overcome that if there is no place to stand.

 

[ichabod]

I was actually going to try something very similar, so I would be interested in hearing how it works out for you.

 

[Oofta]

I almost always have minions in my boss fights, especially at higher levels. I just ran a session for 19th level PCs with a slightly modified kraken and threw in a couple of also slightly modified molten magma ropers. The kraken is CR 23 and the ropers are only CR 11; taken individually the ropers don't add a ton to the fight, they still couldn't be totally ignored. This was after they had already had a few encounters without a long rest, so it was a hard fight but not intended to be a truly deadly one. It worked well for my group.

So specifically for a dragon, a main thing is to not treat them as melee brutes. They will not last long if they just land and go mano-a-mano. Instead they will use hit-and-run tactics, try to split the party, probably focus fire on whichever PC they perceive as weakest.

At the same time, you want to make sure you're engaging your players and ensuring that most of the time they can do something with their PCs that at least has a chance to contribute to the game. Easiest is to just make sure everyone can fly or has effective ranged attacks.

Another possibility is a lair full of traps. Make it so that some of the traps can be countered by something other than a disable device. For example the group is fighting the dragon opens a dam, water is flooding out. Maybe the fighter can get to and pull down a large rock to cause a small avalanche to redirect the flow or the wizard can cast a wall of force to stop the flow. The tricky thing here though is knowing the group and how much you're going to have to broadcast options.

You can always use things like Fizban's greatwyrms which have CRs in the upper 20s but they kind of just look like they could just be a massive bag of hit points.

It's also okay to have things that are a bit contingent on how well the group is doing and what they're enjoying. As a general rule I never change anything once initiative is rolled but this is an unusual situation. I have a pretty good handle on what the PCs in my group can do because we've gotten to 20th level through play. But a one shot is going to be tougher.

So consider adding reinforcements, traps and hazards that may expire or be added as needed. If a particular hazard is being super annoying, give the group a free check for them to realize there's a way they could shut it down or, with a bit more effort, turn it to the group's advantage. Have the dragon bring in reinforcements. Consider having goals other than just killing the dragon.

Good luck with this, having encounters that are both engaging and threatening is difficult at all levels, it's just a different kind of challenge.

 

[Uni-the-Unicorn!]

I want to run a one shot of a party of 5 20th level PCs versus a powerful dragon in its lair. While I have been running (and designing for) 5E for all of its life, I have never run 20th level before.

A few context notes:

PCs will be custom built for the fight, with access to PHB, Xanathar's and Tashas.
It will be one shot without a lot of story, focused on the tactical experience.
It will be played on Fantasy grounds, using a grid, line of sight, etc.

The experience I am going for is very difficult but fair, and fun.

My biggest concern is action economy. I am thinking of combining minions with terrain to make sure the PCs can't just gang up on the dragon.

Thanks for your help.

How will the party be equiped? What magic items will the have? That makes a difference at these levels

 

[Uni-the-Unicorn!]

Also, lair actions are your friend!

 

[dave2008]

Well this is right up my alley! I would love to help and I have run this exact scenario before (but 7 years ago +/-). I am getting ready to a day full of meetings so I will get back to you tomorrow with more detail. However, I would say for the encounter with the dragon itself, you don't have to have minion with a well designed dragon and lair actions. Minions are good in the cavern / lair complex itself, but I prefer my climatic dragon battles to be true solos and design them as such. More to come!

 

[Reynard]

How will the party be equiped? What magic items will the have? That makes a difference at these levels

I will give them set number of items of different rarities and let them submit a list that is subject to veto. Note that I am pulling players froma decent sized pool of folks with whom I have played before, some for decades, so I have a sense of what to look out for. I will also be seeking advice here on anything character creation wise that gives me pause.

The basic premise is that the PCs are not just general adventurers, but specifically dragon hunters. They will be expected to build their characters as such. However, they will not know before play what type of dragon they are going up against or where/what its lair is. I am likely to use a 3rd party source for a non standard dragon and its minions.