Help me construct an actually-deadly devil encounter

[Chronos]

In the next session or two, it might (or might not) come to pass that my players will have an encounter with a group of devils. If this happens, they will know that they will be encountering devils, and when, probably with several days' advance notice, and that it will in all likelihood be the only combat encounter they will have in that entire day. And I want this encounter to be hard enough that, if they don't seek help with it (which they will have ample opportunity to do), they will probably lose.

I don't have enough experience DMing to know just what sort of encounter this would take. I've heard that what the DMG calls a "deadly" encounter just means that a party needs to put in an actual effort, and that you need to go several times that if you want a significant risk, but I don't know how many times that. As a further complication, my party is larger than typical, at six (a barbarian, fighter, hexblade, cleric, druid, and wizard). They'll all be level 5 at the time of this encounter.

If anyone's curious, the most likely source of help they would seek would, effectively, be an untargetable druid with an unlimited number of 3rd-level spells, who would use those spells primarily for healing, buffs, terrain control, and other support. But there are a number of other sources of help they could recruit instead, or possibly in addition. And they will also have the opportunity, should they pursue it, to avoid this encounter entirely.

Ideally, the encounter would be better with fewer powerful devils, rather than a large number of weak ones, just because there are going to be a lot of folks in play, rolling a lot of dice, and I don't want the players to have to wait too long between their turns. But I realize that that can lead to swingy combats, so if it's not viable to balance it that way, so be it.

So, what's a good calibration point for this encounter?

[Chaosmancer]

Keeping everything below CR 10, my first thought is to use Chain Devils who have an obvious and less obvious nasty effect.

The Obvious one is using the Unnerving Mask (I would ignore the "dead loved one" part personally) to frighten a party member that starts near them, preventing them from closing and giving disadvantage if they are next to them.

The less obvious thing is their animate chains, specifically that the chains animated stay animated until one of two things happen. The devil is incapped. The chain is reduced to zero hp by being the target of an attack (they are objects, not creatures, so AOEs won't hurt them usually). Since these devils are in a prepared location, it is very reasonable that the Chain Devils have already animated chains, and have them within reach. This gives them six attacks of 2d6+4, each attack having reach and auto-grappling, the grappling preventing the chain from attacking, but automatically dealing 2d6 to the creature at the start of the turn.

With proper positioning and a little luck on the devil's part, three of these guys could be dealing potentially 6d6 to every party member, every round.

I once had a single chain devil taking on a full team of level 5's as part of a one shot at Origins, and it was a tough fight usually (though the party did have limited access to magical weapons). Two or Three of them? Deadly, in my estimation.

If you want one of them as a boss, then you can add in a handful of Barbed Devils too. They have a ton of hp (110), can make three melee attacks each or two ranged attacks.

So, I'd say 3 chains and 4 barbed are the biggest "oh god we are going to die" if they all get max attacks near melee range, that is thirty attack rolls against the party a round. With an average damage output over 200 hp.

CRs 5 and and 8, and I didn't even find a spellcasting monster.

[Chronos]

To be more clear: It'll be the party choosing the location of the encounter, not the devils (and the choice of location will have an effect on what help they can call on). Given my group's proclivity for doing the last thing one would expect, they could choose a location with a lot of chains... but that's going pretty far even for them.

[Torpin]

i personally treat devils like a very rigid and structed army, so here is what I would do
Have the devils in the middle of cross planar communication with its superior, this allows you to make it a lower initial CR encounter, then have reinforcements come over other round, and then base the reinforcements on how well or poorly the party is doing

[Chaosmancer]

To be more clear: It'll be the party choosing the location of the encounter, not the devils (and the choice of location will have an effect on what help they can call on). Given my group's proclivity for doing the last thing one would expect, they could choose a location with a lot of chains... but that's going pretty far even for them.

By choosing the location do you mean they are luring the devils into a location from somewhere else? Then it still works. Chain Devils can bring extra chains with them, and have them animated and ready to go. 10 ft of chain is only like, 5 lbs? they can easily carry that and of course they would. And, since they chains stay animated until the devil ends up sleeping, they can prepare them ahead of time.

I was more talking about the fact that the devils aren't getting surprised right out of a portal. It is way harder to set up a "you will die without help" level challenge if the players are ambushing the enemy before they have anytime to get their bearings.

[Chaosmancer]

i personally treat devils like a very rigid and structed army, so here is what I would do
Have the devils in the middle of cross planar communication with its superior, this allows you to make it a lower initial CR encounter, then have reinforcements come over other round, and then base the reinforcements on how well or poorly the party is doing

Well, the issue with this is that the OP wants it so the fight is obviously going to be a loss for the party if they do not ask from help from some NPCs.

It also sounds like the party is choosing the battleground here.

Which means they wouldn't be in contact with a higher up when the fight starts, they'd just send what they have.

[Angelalex242]

Well. I'd remember the Devils don't find ending lives very useful. They want souls.

So if the party does something dumb and loses, they have to sign a contract...

But if you want to make it obvious they need help, well, nothing says "You're outclassed" Like a Pit Fiend standing there. Or, if they're level 5, even an Ice Devil.

[Chaosmancer]

Well. I'd remember the Devils don't find ending lives very useful. They want souls.

So if the party does something dumb and loses, they have to sign a contract...

But if you want to make it obvious they need help, well, nothing says "You're outclassed" Like a Pit Fiend standing there. Or, if they're level 5, even an Ice Devil.

Yeah, but that gets so obvious. And they are supposed to be able to win with help. Which just leads to "our level 5 party beat a pit fiend" style stuff

[MaxWilson]

My rule of thumb for deadly combat is that if you consider all player abilities including those that don't show up in CR calculations like extra movement speed, "CR ~= level" is basically true after about 5th level.

Your PCs are low enough in level that I would soften that just slightly, and aim for five enemies instead of six.

I nominate three Merregons and two Black Abishai. (Merrogons help protect the Black Abishai's concentration so Darkness remains intact--all five fiends benefit. Also, the Merregons get extra attacks when led by Abishai.) Add an extra Black Abishai if the PCs have fought devils before and know their traits, or have some other way to know their enemy.

[SLOTHRPG95]

One bone devil, backed up by two barbed devils and two bearded devils. The bone devil sends the cannon fodder bearded devils to rush the party's front-line combatants, while the barbed devils maneuver around to attack any backline casters, possibly hurling fire along the way if they're forced to move through difficult terrain put in place by the druid, or other obstacles. The bone devil takes to the sky on its first turn, and then divebombs casters concentrating on juicy spells like Haste or Spirit Guardians. With a party of six plus support, and good tactics, this should be winnable. But without backup or with sloppy tactics, the backline casters lose their buffs/BFCs, and the party ends up encircled.

[Chronos]

Quoth Angelalex242:

But if you want to make it obvious they need help, well, nothing says "You're outclassed" Like a Pit Fiend standing there. Or, if they're level 5, even an Ice Devil.
Wouldn't work. They would know in advance they would be facing devils, but not which ones. They'd only know what it is once it shows up, and that's not the time for them to start seeking help, if they haven't already.

MaxWilson, I don't see merregons nor black abishai in my Monster Manual. Though something that can cast Darkness would be a good idea, given that they can all see through it (you'd think that casting Darkness would be a more common devil ability).

[J-H]

Give them some spell scrolls or wands or a way to cast spells. Otherwise, you're setting up a bruiser fight with the players having spellcasting and the enemies having none.

I'd consider a single Ice Devil for the Ice Wall spell (note - damage is high, try not to kill anyone - use it to split the battlefield and force decision-making), and several Imps because the Imps can go invisible and harass the back line, plus whatever else you pick.

[No brains]

Since it looks like you have a decent number of bruisers supported by healers, a pike square of bearded devils could put the fear of Asmodeus in them. 2.5-3.5 bearded devils per character could stack up the bleed damage and the 'can't recover hp' effects. While the bleed damage has the opportunity to run away into being deadly, you could soften the encounter by having the devils under orders to give the players the option to flee. (That may not work if the players get to choose the battlefield, but see what your DM mind can think of.)

Weirdly enough, barbed devils greatly benefit from being on watch towers with their high perception and decent range. Making the players climb to engage enemies who can hit them hard could take the wind out of their sails.

A swarm of spined devils can fly straight over the bruisers and spike the party in descending order of squishiness. Drop the wizard, then the druid/hexblade, then maybe the barb or cleric. The limited tail spines feature of spined devils gives you a reason to hold back and have the devils disengage before the party gets too hurt.

[Chaosmancer]

Wouldn't work. They would know in advance they would be facing devils, but not which ones. They'd only know what it is once it shows up, and that's not the time for them to start seeking help, if they haven't already.

MaxWilson, I don't see merregons nor black abishai in my Monster Manual. Though something that can cast Darkness would be a good idea, given that they can all see through it (you'd think that casting Darkness would be a more common devil ability).

Mordenkainen's Tome of Foes is where those are from. Added a lot of decent devils and demons

[Angelalex242]

Ya know, scouting is a thing.

Have a friendly NPC wizard say, "Ya know, I scryed those devils of yours when I heard you talking about them, and...there's an ice devil. You guys are straight up out of your league. You'll need some help."

[kazaryu]

In the next session or two, it might (or might not) come to pass that my players will have an encounter with a group of devils. If this happens, they will know that they will be encountering devils, and when, probably with several days' advance notice, and that it will in all likelihood be the only combat encounter they will have in that entire day. And I want this encounter to be hard enough that, if they don't seek help with it (which they will have ample opportunity to do), they will probably lose.

I don't have enough experience DMing to know just what sort of encounter this would take. I've heard that what the DMG calls a "deadly" encounter just means that a party needs to put in an actual effort, and that you need to go several times that if you want a significant risk, but I don't know how many times that. As a further complication, my party is larger than typical, at six (a barbarian, fighter, hexblade, cleric, druid, and wizard). They'll all be level 5 at the time of this encounter.

If anyone's curious, the most likely source of help they would seek would, effectively, be an untargetable druid with an unlimited number of 3rd-level spells, who would use those spells primarily for healing, buffs, terrain control, and other support. But there are a number of other sources of help they could recruit instead, or possibly in addition. And they will also have the opportunity, should they pursue it, to avoid this encounter entirely.

Ideally, the encounter would be better with fewer powerful devils, rather than a large number of weak ones, just because there are going to be a lot of folks in play, rolling a lot of dice, and I don't want the players to have to wait too long between their turns. But I realize that that can lead to swingy combats, so if it's not viable to balance it that way, so be it.

So, what's a good calibration point for this encounter?

depending on how much you're willing to homebrew...

i mean, chain devils+darkness nearly wiped a party i was in of like, lvl 12+ people. most of us casters..but like the tanky cariety (2 multiclassed cleric bards and like..a paladin i think?) point being that we had jack all ability to deal with the darkness (i dispelled, but they just..recast it so...) i do notice that someone already suggested the darkness spell and honestly...its just, one of the easiest ways to give PC's a massive debuff, and its useful regardless what level the PC's are.

[da newt]

A single Chain (or Bone Devil boss) with a handful of Bearded / Barbed / Spined Devil cohorts with a few Imps should be plenty challenging for an average party of 6 5th lvl PCs. If the devils fight intelligently, this is plenty difficult.

If your party is highly skilled in tactics/combat add an Erinyes boss who stays out of melee.

The very simple answer is add devils. The more attacks and targets that you bring to the fight, the more deadly it is. A handful of invisible Imps can make s big difference.

Now for CR math:

6x lvl 5 PCs -> deadly XP threshold = 1100 * 6 = 6,600

Chain (3,900) + 5x Spined (450) + 5x IMP (100) = 3900 + 2250 + 500 = 6,650
(ignoring the number of monsters multipier for ~10 total bad guys = *2.5)