Devils occupy the lawful end of the fiend spectrum: demons occupy the chaotic end. Unlike devils, which rarely stray onto the prime material plane except on a mission of malice, demons like to exploit holes in the cosmic fabric, popping through to ruin things for everyone on the other side. Thus, an adventuring party is much more likely to stumble upon a random demon than a random devil. There’s also the possibility that a demon has been summoned as a servant or ally by an evil spellcaster but broken free of its bonds.
Advanced Dungeons and Dragons numbered demons by type, but by the second edition, descriptive names were already supplanting numbered types (2E didn’t even use the word “demon,” probably cowed by rampaging fundamentalists). Fifth-edition D&D brings back the numbered types, but they take a backseat; each variety of demon is referred to primarily by name.
One trait that all demons have in common—which is described in the Monster Manual flavor text, not in their stat blocks—is that they can’t be permanently killed on any plane except the Abyss. If the player characters destroy a demon on their own home plane, that demon isn’t killed, merely dispelled, and it immediately re-forms in the Abyss in a nasty mood and with a new grudge.
The upshot of this, from a tactical perspective, is that demons don’t fear death and have no self-preservation instinct that will induce them to back down from a fight, even after taking substantial damage. Only in the Abyss, or if its essence is contained in a demonic amulet that the PCs possess or might be able to get a hold of, will a demon exercise anything that might be described as caution.
Another feature common to all demons is that they’re either resistant or immune to cold, fire and lightning damage and immune to poison. They also have either darkvision or truesight, indicating a preference for operating in darkness, where characters without darkvision or a light source will be at a disadvantage.
Manes (may-neez) are spirits of the evil deceased, demonic analogues to lemures. They’re shapeless and weak, but unlike lemures, they’re occasionally summoned to wreak havoc on the material plane. There’s little to say about them, though: they’re stupid and slow and neither unusually strong nor unusually agile, and their only combat ability is a melee attack with their claws. Point one in a certain direction, and it will lurch forth and dully try to shred whatever it runs into. Hardly worth bothering with, honestly.
Even type 1 demons, however, represent a substantial leap upward in threat level. Type 1 includes shadow demons, barlguras and vrocks, with challenge ratings of 4, 5 and 6; in contrast, manes are CR 1/8.
Shadow demons not only possess darkvision out to 120 feet but also have Light Sensitivity, which penalizes them in bright light, and Shadow Stealth, which lets them Hide as a bonus action in dim light or darkness. Other demons prefer darkness; for shadow demons, avoiding the light is an imperative. If a PC casts a spell that creates bright light, a shadow demon will shrink from it. Shadow demons are vulnerable to radiant damage as well, and if struck with it, they’ll be simultaneously enraged and terrified, and they’ll do whatever they can, short of fleeing, to avoid the enemy who inflicted it.
Shadow demons’ physical ability profile is that of a skirmisher. Their claw attack does two extra dice of damage if they have advantage on an attack roll—similar to a rogue’s Sneak Attack. Combining this with Stealth proficiency and the ability to Hide as a bonus action, we have the elements of a tactical combination: the demon Hides in darkness, giving it advantage on its first attack from hiding and thereby boosting its damage. This gives away its position, however, so we have to figure out how it gets back into hiding to strike again.
The answer may be, it doesn’t. Although its resistance or immunity to every type of damage except radiant damage and physical damage from magical weapons gives it some defense against opportunity attacks, it simply isn’t fast enough to get out of its opponents’ sight. Even accounting for Incorporeal Movement, which lets the demon pass through the opponent it’s just attacked and keep going, we have to assume that the opponent has the time to turn around in order to make the opportunity attack to which he or she is entitled. The only way for the shadow demon to Hide would be for it to pass beyond the distance the opponent can see. In the case of a PC with darkvision, that’s 60 feet; in the case of a PC without darkvision but with a light source such as a lantern, lamp or torch, it’s at least 40 feet. In either case, the shadow demon can’t move nearly far enough in one turn—at least, not without Dashing.
I think we have to conclude, therefore, that shadow demons prey on the weak. They choose the opponent with the fewest hit points (with Intelligence 14 and Wisdom 13, they’re able to judge this accurately) and strike fast and hard, in the hope of finishing off the foe in one or two rounds at most. If the first blow doesn’t do at least severe damage (60 percent of the opponent’s maximum hit points), or if the second doesn’t finish the opponent, the shadow demon uses its next turn to Dash (action) away, potentially subjecting itself to one or more opportunity attacks, then to Hide (bonus action) once it’s beyond its opponents’ sight. While hidden, it maneuvers around stealthily until it can creep up on its victim again. It’s not fleeing when it Dashes away, only repositioning, and it may fly for part or all of its movement. It repeats this sequence until either it or all its opponents are defeated.
Barlguras are dumb brutes, but they’re dumb brutes with some interesting capabilities. For one thing, they’re actually proficient in Stealth, and this combined with their Running Leap feature gives them a potent surprise Multiattack, albeit not one from hiding (it’s hard to miss a large, red demon-ape barreling through the air toward you) and therefore without advantage on the attack rolls. But wait, there’s more! They also have Reckless, identical to the barbarian class feature Reckless Attack, which grants them advantage on all their attacks in exchange for advantage on attacks against them. Given their Intelligence of 7, I’m inclined to think they use this feature all the time, even when they don’t need to. It’s just part of their demonic nature.
How much would you pay? Don’t answer yet! Barlguras have innate spellcasting ability, and one of their innate spells is invisibility. They can attack from hiding after all! Would they, though? Are they smart enough to? How would a basically stupid creature employ spells like disguise self and phantasmal force, which are most effective when used with creativity? What’s a good way to make use of these spells that will work in most cases without any kind of variation, since they don’t have the Intelligence to adjust their strategy from situation to situation?
Here’s one idea: Barlguras use phantasmal force to create an illusion that will draw victims to it, such as a pile of treasure, a table piled with food, a cute baby animal. Then they lie in wait, hidden. When a group of victims approach to examine the illusory bait, the barlguras cast entangle beneath them, restraining those who fail their Strength saving throws. Then they come barreling in and start attacking Recklessly. (If there are multiple barlguras in the encounter—the flavor text says they often roam in packs—just one of them casts entangle, while the others take advantage of the element of surprise. If there’s only one, its attack won’t be a surprise anymore once the PCs have already found themselves suddenly entangled by magical vines.)
In an encounter like this, it’s important to keep track of what advantages and disadvantages both the barlguras and the PCs possess, because they’re going to stack up, but any and all advantages cancel out any and all disadvantages, and vice versa. Barlguras may have advantage from attacking from hiding (though probably not), from Reckless, from attacking a restrained opponent and/or from attacking a blinded opponent (one who can’t see in darkness). PCs may have advantage from attacking a Reckless barlgura, and they may have disadvantage from being blinded and/or being restrained.
[Edited to add: The barlgura has a listing in the MM errata. Both its regular and climbing speeds should be 40 feet.]
Vrocks are flying brutes with 60 feet of flying speed and resistance to physical damage from normal weapons. Therefore, they can hover in the air, fly into melee, attack, then fly back out of reach; they may incur one or more opportunity attacks in doing so, but they’re not overly concerned about that.
The question with vrocks is which of their attacking actions they use on any given turn: their melee Multiattack, their Spores or their Stunning Screech. The Stunning Screech can be used only once per day, so let’s look at that first. It can stun creatures within a 20-foot radius, but for only one round. A stunned creature automatically fails Strength and Dexterity saving throws, attacks against a stunned creature have advantage, and a stunned creature can’t move or take actions or reactions. The radius of Stunning Screech suggests that it should affect four enemies, on average (based on “Targets in Area of Effect,” Dungeon Master’s Guide, page 249). So whatever is going to happen to the stunned victims has to happen within the next round, or the opportunity is wasted.
The MM doesn’t say whether vrocks hunt in flocks; if they do, they stand a much better chance of getting some real benefit from a Stunning Screech. Vrocks may also be summoned by more powerful demons that can take advantage of their enemies’ incapacitation. For a lone vrock, though, this feature hardly seems worth the bother.
Vrock Spores, on the other hand, poison enemy creatures and can potentially continue to do damage round after round, as well as imposing disadvantage on the poisoned creatures’ attack rolls and ability checks. This one’s a no-brainer. Whenever vrocks have the Spores feature available and can position themselves to affect at least three enemy creatures, they’ll use it.
Next: type 2 and type 3 demons.