Combat rating 3
1 Spined devil (CR 2)
1 Magma mephit (CR 1/2)
3 Smoke mephits (CR 1/4)
1 Steam mephit (CR 1/4)
Combat rating 3
1 Spined devil (CR 2)
2 Harpies (CR 1)
Combat rating 4
2 Spined devils (CR 2)
3-4 Shadows (CR 1/2)
3 Skeletons (CR 1/4)
Combat rating 5
2 Spined devils (CR 2)
1 Scarecrow (CR 1)
1 Cult fanatic (CR 2)
2 Swarms of bats (CR 1/4)
How to Use – Combat Encounters
Before I begin, let me say that there is no reason that the spined devil would ever make a melee attack. Its spines are far more powerful, and it will not run out. No fight ever lasts six rounds unless it is the big, final boss, and the spined devil is not a boss.
I would have the spined devils be constantly moving, just because it feels appropriate. They might fly close to the ground [I can’t explain why, but it feels right] but they’ll keep out of the range of most melee PCs. I guess a monk might surprise them once, but not twice. The PCs might try using dash to close the distance, but that will leave them without an action, and the spined devils have free disengage thanks to flyby.
If I wanted to get them into melee, I would have one of them use an attack to knock the melee fighter[s] prone, and then several of them could swarm him, gaining advantage on melee attacks. Even this doesn’t make much sense. (The melee are the last PCs they would target. The casters are a far greater threat, and far more vulnerable.) It would have to be to distract from a threat to the spellcasters.
If you have a lot of them [minimum 8] you could have four of them attack the melee and the others attack the spellcaster. A better bet would be to combine them with a single CR 5 or higher, who is taking advantage of this to tear into the spellcasters. This strategy also requires that the spined devils managed to draw the melee a sufficient distance from the spellcasters in the first place.
Having the fight be taking place indoors would help, as the spined devils can’t fly out of range of the melee, and therefore there is motive for the melee to approach.
Combat encounters (difficulty 4)
The easiest way to add difficulty to a spine devil encounter is if the landscape around is somewhat fragile. Mountain canyons, with loose cliffs, are the easiest choice. If the PCs fling spells or ranged shots about too freely, they’ll bring an avalanche down on their heads.
To run an avalanche without automatically killing the PCs, have only a small section of the cliff collapse. This will be enough to reduce visibility [which might help the players, come to think of it] it will block movement in some areas, render other places difficult terrain, and will release falling and rolling boulders which might damage the PCs if they don’t make a DEX save.
Other areas where flinging magic and missiles carelessly might hurt the players are places where the footing is limited, such as on a frozen pond, when fighting to take a [rope] bridge, or if they’re fighting on top of a forest canopy or on a maze of platforms.
You could also have them be fighting in an area of flammable objects and burning torches, where destroying too loosely could set the place on fire; among levers that if smashed will trigger various traps; or among several valuable but fragile objects, such as spellbooks.
Combat Encounter 2 (difficulty 4)
The Monster Manual tells us that spined devils are used as messengers. As such, another idea would be that the players get told of a message that is going to be sent, and they have to intercept the messenger.
I would suggest three spined devils for this one. The one in the center will be carrying a scroll, and the other two will be guarding him, although they might retrieve the scroll the messenger is killed. It should probably be recognizable which one is carrying the message.
Note that the difficulty of this scenario will obviously vary considerably depending on how important it is for them to capture the message, or just to prevent its delivery. If you’re going with preventing its delivery, I would have all the spined devils be carrying messages, so that if just one of them gets through the players will have essentially lost. It is possible that the devils will fight to defend each other, if they think they might win, or that one of them will be of greater importance, to the extent that the others will fight to defend him. You can have him wearing something to mark his importance.
You can increase the difficulty by not letting the players know beforehand that the messengers are going to be flying. If so, I would have the canyon be narrow at the top, and provide some reason why the spined devil wouldn’t react by flying up in response to the ambush. If there is some reason that they’ll worry about ranged units, or flying units, or if the devils are trying to keep their presence low-key, those might be good reasons.
To make it easier, if you see that your players are not going to manage, you could have the spined devil carrying the message dodge into an alcove in the cliffs. Perhaps because it panicked, perhaps because they’re carrying something too important to risk losing. One of the spined devils will go back for reinforcements, any others will fight to defend the alcove. Depending on where the alcove is located, it is very likely that the players will have to climb the cliff, and possibly contend with sheer rock face and/or loose rocks in getting to it. You might want to decide on a time limit until the reinforcements arrive, as without that it will be a fairly easy encounter.
In this version, you’ll want it to be important to capture the message, or to have the devil be transporting an important item. Otherwise, they might collapse the cliff on the devil.
(This isn’t a combat encounter, but it is a valid way to use spined devils.)
The Monster Manual tells us that spined devils are also used as spies. I don’t know what the writers have in mind, as it’s hard to imagine why the Nine Hells would want to use spined devils for that when imps can turn invisible and shape change, but spined devils would make excellent sentries.
I would use this as a part of a dungeon, giving the spined devils a cave high up somewhere near the center of the dungeon, and using it to force the players to only moving around in areas where there is cover. You can also, as a way to introduce variation, have a brief period where bad weather allows the players to move more freely, with the catch that they might be stuck in the wrong area of the map if it clears unexpectedly, or when they’re indoors.
They might also think of other strategies that they can use, such as using a decoy or an illusion to draw the spined devils’ attention to a different part of the map, letting they make a dash for a certain location.
Any time that the spined devils find them will lead to the spined devils joining the fight, if outdoors, or inflict not-insignificant damage on them before they reach their location, if indoors. They can also lead other monsters to join the fight.
I would have the fights become somewhat difficult as a result of this [they’re supposed to be motivated not to get into this situation], but don’t kill them. Make sure that they have the means to retreat. They might occasionally win in spite of the spined devils, especially if they set themselves up to be ready for them.
Depending on how it goes, you can either increase the difficulty next time, as the spined devils learn not to take the PCs lightly, or you can decide that the spined devils are defeated, and stop using them as sentries. Setting up an ambush is a legitimate way to get rid of a threat, and that is what your players are doing.
They might also figure out a way to sneak up to the cave and attack the spined devils there.
If they don’t get rid of them on their own, consider letting them discover a ledge or a tunnel that goes up to the spined devils’ cave, giving them an opportunity to get rid of them. It will be very popular with the players.
A ledge is obviously the harder way, as they might only be able to go in single file, there might be places where they have to climb, and the spined devils will be hassling them the entire way with their spines and by dropping rocks on them and the like.
There is also a good chance that they’ll enter into melee to prevent the PCs from advancing any further, especially if they can find a good spot where they’re safe from ranged attacks and where the path is too narrow for more than one PC at a time. For an even harder situation, have the spot be on the other side of a place where the players have to jump or climb. To prevent the spined devils from running away as the PCs reach the top, I would put an item or the like of quest significance that the devils are determined to defend.
(If using a tunnel, you can still have places where they need to climb or jump, but I’d use other monsters to defend the far side, if you want to do that.)
With a tunnel, you can have the spined devils attempt to escape, as the PCs will be on them unexpectedly and will therefore have a chance to take and hold the entrance. The PCs will need time to prepare after they know that they’ve reached the end of the tunnel, and you might want to point out to them the need to prevent the spined devils from fleeing.