D&D 5E Final Boss (tm) for a level 11 campaign.

[DeviousQuail]

IME that is a perfectly fine final boss as long as it's not a surprise to the party. If they have no idea it's coming then don't be surprised if a Legendary CR 17 runs roughshod over them. The caveat here is that this isn't the first encounter of the day and you as the DM play the boss like it wants to survive>win.

 

[Charlaquin]

Thanks guys for the answers
Actually my question is more about the "Legendary C17 monster" and less about the "Adult Red Dragon" : i could have ask the same question about the Androsphinx, for example.

Is (CR17+Legendary) well balanced enough for a perfect climax (against 4 level 11 PC) ?

So, the thing to understand about CR is that it really only cares about how much damage the monster can deal in the number of turns it’s expected to be able to survive. The frame of reference the system is built around is one monster against 4 PCs of a level equal to its CR, dealing about a quarter of the party’s total HP in damage before it dies. Typically, that projection is based on its average damage over the course of 3 rounds, but some monsters deal higher damage and last fewer rounds, while others do less damage but last more rounds.

A CR 17 monster, then, can be expected to deal roughly a quarter of a 4-person, level 17 party’s health in the time it’s expected that such a party will take to kill that monster. Having Legendary Actions doesn’t typically affect its CR, unless those Legendary Actions allow it to survive more rounds or to deal more damage on average over the course of the number of rounds it’s expected to survive.

How does this translate to a fight against a level 11 party? Well, kind of awkwardly. The amount of damage the monster can deal is going to be a fair bit higher relative to the party’s total HP, which means a very high risk of randomly one-shotting a character on a lucky roll. Additionally, there are certain levels where party average DPR spikes. Those levels are 3rd, 5th, 11th, and 17th. So, putting a party of 11th level characters against a CR 17 monster means their average DPR is going to be significantly lower than the CR system expects it to be. So the monster has a high chance of being able to survive an extra round, or maybe two if the players roll poorly.

Now, it sounds to me like what you’re looking for is a challenging but fair fight, and in my opinion, simply putting the party against a single monster that’s several CR above their level isn’t likely to deliver that. Either the party will get lucky with their rolls, in which case the monster won’t be a huge challenge for them, or they’ll get unlucky (or if the monster will get lucky) and they’ll get curb stomped. There isn’t a lot of middle-ground.

If what you want is a challenge that is tough, but not so swingy, you would be better off using a boss monster closer to the party’s CR (between 9 and 13, probably) and give it minions that are well below their CR. That will increase the total damage output on the monster’s side, without putting the boss monster’s damage output high enough that you risk accidentally one-shotting anyone on a lucky roll, and it will keep the number of turns the boss itself can be expected to survive when the party focuses fire on them in that 2-4 range, while providing speed bumps in the form of those weaker monsters, which will more likely only survive one or two hits.

 

[jgsugden]

....
If that's the first roll, sure it's boring. But if half an hour of combat leads up to it - pretty cool!

Which ... would be why ... the legendary resistance would be a good idea. To delay that save so that it doesn't happen on rd 1.

 

[Flamestrike]

Hi guys !

From your play experience, is an Adult Red Dragon (CR 17 Legendary monster) strong enough to fight all alone against a solid (but not optimized) party of 4 level 11 PC et provide a fun and challenging experience ?
If it's not, wich (CR + Legendary) combinaison would be better suited ?

Thanks for your help

How many encounters have they had that day, and what magic items do they possess?

 

[THEMNGMNT]

Lots of good advice here.

In my experience, 11th level PCs are extremely resilient. I'm confident that they can defeat a CR17 red dragon. It's even possible they'll do so quickly and easily. I think the challenge for you is to find ways to extend the fight so that it's long enough to be satisfying. Definitely use legendary actions and lair actions. Consider using terrain in combination with a multi-stage fight.

For example, maybe the dragon's lair is in a volcanic cave. Each turn, something happens in the cave...an eruption of lava, a collapse of a stalactite, an earthquake. The cave itself is filled with crevasses, stone shelves, stalagmites and stalactites which give the dragon many places to strike from or take cover in. In the first phase, the dragon confronts the PCs at the front of its cave. When the dragon reaches half hit points, give it a special "bloodied" ability. For example, as a free action it can disengage and fly away without taking opportunity attacks...or it brings down the roof of the cave to knock all enemies prone while it flies off, etc. In the second phase, minions and allies swarm in from connecting passages. In the third and final phase, the dragon makes a last stand in the back of the cave, atop its treasure hoard, where the volcanic heat and gasses cause automatic, ongoing damage.

Each phase will be challenging for the players, but they'll get a chance to heal or buff in between phases if needed.

 

[Stalker0]

The amount of damage the monster can deal is going to be a fair bit higher relative to the party’s total HP, which means a very high risk of randomly one-shotting a character on a lucky roll.

So this is where 5e's HP cushion really comes into play. In order to one shot a PC, once its at 0 you have to deal damage equal to its HP or higher. So an 11th level wizard, assuming a +2 con (which I have found pretty typical in my games), has 68 hp, not factoring in spells like false life or aid, etc.

The breath weapon of a 17th level dragon does 63 damage on average, assuming a failed save. So if a character is fully knocked out, then the dragon has a chance to kill it in one shot (roughly 27% as a matter of fact). Now if the character has any hp remaining before the attack, or has any basic protection magics to give a little temp hp....then the wizard will be down but just fine. Example just adding the 5 hp from Aid reduces the instant kill chance (and this is assuming the PC is already down) to about 10%.

One shoting PCs is very hard at high levels even when they unconscious, and is basically impossible when they are half health or higher. The far deadly option is for the dragon to use its 3 attacks against an unconscious character. Each hit is an automatic death save, 2 on a crit....that's a far more reliable method than using a single big damaging attack.

 

[Charlaquin]

So this is where 5e's HP cushion really comes into play. In order to one shot a PC, once its at 0 you have to deal damage equal to its HP or higher. So an 11th level wizard, assuming a +2 con (which I have found pretty typical in my games), has 68 hp, not factoring in spells like false life or aid, etc.

The breath weapon of a 17th level dragon does 63 damage on average, assuming a failed save. So if a character is fully knocked out, then the dragon has a chance to kill it in one shot (roughly 27% as a matter of fact). Now if the character has any hp remaining before the attack, or has any basic protection magics to give a little temp hp....then the wizard will be down but just fine. Example just adding the 5 hp from Aid reduces the instant kill chance (and this is assuming the PC is already down) to about 10%.

One shoting PCs is very hard at high levels. The far deadly option is for the dragon to use its 3 attacks against an unconscious character. Each hit is an automatic death save, 2 on a crit....that's a far more reliable method than using a single big damaging attack.

Ah, sorry, I should have clarified that by “one shot” I meant bringing a character from max HP (or whatever HP they started the fight at) to 0 in one hit, not causing instant death by dealing Max HP damage to a character at 0 HP.

 

[Stalker0]

From my own experience: I was able to barely TPK a group of (6) lvl 10 PCs with a CR 19 balor, so I think CR 17 monster for your group should be a good challenge.

I'll also note that in my experience the number of players is a major force multiplier. I would argue that 6 lvl 10 PCs, all else being equal, are about 60% stronger than an equivalent level party with 4 players. That does very on the encounter, encounters with more area effects will favor a smaller and stronger party, where big bad scenarios favor lots of players with lots of actions.

 

[Quickleaf]

Thanks guys for the answers
Actually my question is more about the "Legendary C17 monster" and less about the "Adult Red Dragon" : i could have ask the same question about the Androsphinx, for example.

Is (CR17+Legendary) well balanced enough for a perfect climax (against 4 level 11 PC) ?

Actually, the specific monster matters immensely.

Disclaimer: I have only run a handful of dragons (and a dracolich) in straight up combat in 5e, but I've played in a dragon-slaying series my friend DMed. And I've used dragons thematically and in roleplaying encounters (even an exploration encounter inside a dead dracolich) a whole lot.

One guideline I use as the "you must be this tall to safely enjoy the ride" bar... as my personal litmus test for whether a monster I'm thinking of using might be too powerful... is I look at the monsters damage output in a single turn (both single-target & area effect), and compare that to the average HP of the PCs.

If multi-target damage in one turn can reduce entire party of fresh PCs to 0 HP, that's a red flag.
Similarly, if single-target damage in one turn can reduce a fresh PC to dead (not dying, but dead), that's also a red flag.

So 11th PCs might have an average of 8+(10*5)+(11*1) hit points = 69 HP when fresh. That's a rough number to keep in mind.

An adult red dragon can breathe a 60-foot cone (conceivable getting the entire party) that deals 63 average damage on a failed save. It could almost, but not quite reduce the entire fresh part to 0 hit points in one turn.

However, if its breath weapon was a little closer to the average party HP (e.g. if you'd said a 10th level party, with average 63 HP), then I'd flag the monster as very possibly too powerful in an equal fight.

The adult red dragon's single-target damage in one turn is 26 bite + 15 claw + 15 claw = 56 damage. Probably not going to outright kill a fresh 11th level PC. Checks out.

An androsphinx isn't putting out the same kind of damage as a red dragon; instead its threat comes from more control abilities, game-changing banishment, superior mobility with freedom of movement & teleportation, and some seriously wild Lair Actions.

The androsphinx's flame strike is probably catching 2 PCs with its 10-foot radius, so 2*(8*3.5) = 56 damage. Less than the red dragon, and its not catching the whole party.

Whereas the androphinx's single-target damage, at 2*17 = 34 damage, is much lower than the dragon's.

As a closing thought, I'd encourage you to think holistically about your encounters in a way that goes deeper than comparing CR to level/number of PCs. For example, if the party relies on spells for magical flight to face flying monsters on more equal footing, then the red dragon is at a disadvantage, while the androsphinx (with dispel magic up its paw) suffers no disadvantage and might even turn the tables on the PCs with a nasty fall in store. That kind of thinking will be much more valuable to you than the CR system, at least, in my humble opinion.

 

[Paul Farquhar]

So take a party member out. They pop back up, like moles.

Taking a party member out does not mean reduce to zero hp. Dragons are intelligent, they will make sure they kill a character outright before moving onto another, or use dragonfear and spells to take party members out of the fight without killing them.