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Derro have been in the game since AD&D 1st Edition, where they appeared in the Monster Manual II. They’re based on the writings of an American author named Richard Sharpe Shaver, who wrote a lot about a civilization of psychic and torture-obsessed underground humanoids he named the dero (from “Detrimental Robots”).
D&D Derro have a different origin from Shaver’s dero, though the flavor is quite similar in 4e. When the world was still young, it gave rise to an advanced and power-hungry civilization. Its people, the derro, craved power like that of the primordials, but they wanted to bow to no master. So derro scholars came up with an alternate solution: open a portal to this unoccupied magic-rich dimension they found. There would be no one to contest their claim! Free unlimited power!
They succeeded in opening their portals, but found out this new dimension was far from unoccupied. It was the place known today as the Far Realm. After the derro beheld what came through to greet them, they suddenly realized they had finally found a master worth worshiping. In other words, their sanity was blasted to dust.
Derro civilization became so horrifying in its depravity that the World Serpent, one of the most powerful primal spirits, coiled around it and dragged the entire thing underground. This stopped their grand machinations but did not destroy them. Many centuries later, a drow expedition found the ruins of the derro empire, and what the derro became in the dark. Only one of their number made it home… mostly. Her report convinced the drow these maniacs must be eradicated, but this is harder than it looks.
In our narrative present, derro live in small groups that crawl around the ruins of their old cities, and worship the energies and beings of the Far Realm. They’re enthusiastic slavers, going on frequent raids to the surface or to other Underdark communities to find new captives. They treat these slaves badly, torturing them for fun and killing them for the smallest of offenses. The slaves, in turn, will turn on their captors as soon as the smallest chance to escape presents itself.
Derro are only capable of making true alliances with beings from the Far Realm, suck as grells, mind flayers, and aboleths (whom they sometimes worship). They despise everyone else, and everyone else hates them right back.
Derro are statted up as mid-Paragon threats, suitable for inclusion in encounter groups that feature their preferred allies listed above. The entry also gives enough Derro stat blocks to make decent all-Derro encounters.
Derro are Small Aberrant Humanoids. They have Darkvision, and their signature ability is named Strength of Madness. It’s an encounter power that lets them roll a d6 and add the result to all of their attack rolls until the end of their next turn, but also makes them grant combat advantage during this time.
Combatants like these typically make up the patrols that keep derro territory “secure” by engaging in preemptive attacks against its neighbors. Gotta keep them guessing, y’know.
Warriors are Level 13 Artillery with 101 HP and all standard Derro traits. Their speed is 5, and they have a +2 to saves against fear effects. They carry daggers and a repeating hand crossbows with several magazines.
The dagger is their default melee attack, and they can fire the Repeating Hand Crossbow as a minor action, or use a standard action to let loose a Bolt Spray (recharge 5+) that hits a Close Blast 5 for heavy damage and pushes 1 square on a hit. Any of these will deal extra damage against targets granting combat advantage.
Bolt Spray is not selective, and most derro warriors don’t particularly care if their allies are caught in its area of effect. They’ll use it whenever possible.
This can be a less capable warrior, or just your average civilian psychopath. Derro thugs are Level 14 Minion Brutes and they fight with clubs. Their only special ability is Mad Sacrifice: when the thug misses an attack, it can sacrifice itself to turn the miss into a hit.
Using them in combat is simple: get a whole bunch of them to charge the PCs and hit whoever’s closest, using Mad Sacrifice liberally.
Warriors that display notable skill and potential are invited by Derro savants to peer directly into the Far Realm. Those who remain functional after the experience use this stat block.
Fanatics are Level 14 Skirmishers with 140 HP. They carry battleaxes into combat. Their basic axe attack has an attached effect that allows them to end any mark on themselves and shift 2 squares before making the attack roll.
If they bloody an enemy, their Insane Bloodlust allows them to immediately make another attack against that same enemy. And while a fanatic is themselves bloodied, Unleashed Madness gives them a -2 attack penalty and 2d6 bonus damage.
That effect on their basic attack allows them to slip right past the party’s front line and go for the squishies, and by the time they get there they might even have turned into mini-brutes. Fanatics always fight to the death.
This derro is specialized in capturing slaves, a very important function in derro society. They always need more people to do the labor derro consider beneath themselves, and to act as experimental subjects.
Harvesters are Level 15 Lurkers with 116 HP. They wield war picks and carry a set of shackles. Their attacks do bonus damage if the target is granting them combat advantage.
Their basic attack is a strike with the pick and has no special effects, but they have a frightening power named Harvest. To use it, the derro must have started its turn hidden from the target. It’s an attack against Fortitude, which does no damage but knocks the target unconscious (save ends).
The harvester can them use its shackles to bind the helpless victim, which from that point on is restrained and falls prone whenever it’s hit with a melee attack. The victim can try to escape by succeeding in an escape action against the harvester (Athletics vs. Fort 27, or Acrobatics vs. Ref 28).
If Harvest fails or a victim gets loose, the derro can use Flee to the Shadows, which allows it to move its full speed and make a Stealth test to hide if it has concealment at the end of the movement.
The shackles can only be used once per encounter, but Harvest is at-will. So a harvester could knock someone out, shackle them, and have its buddies drag the victim to their base, keeping them unconscious with multiple applications of Harvest. I guess that once they’re no longer using combat turns, the victim just stays down until they wake up in a cell.
Ironguards are more disciplined than your typical derro warrior, which admittedly is not a high bar to clear. They are proficient in the use of hooked spears, and are often employed to catch runaway slaves or guard them so they don’t run away in the first place. Paranoid derro bigwigs (i.e, all of them) also hire ironguards to watch their stuff.
Ironguards are Level 15 Soldiers with 150 HP. Their hooked spears deal extra damage against prone targets, so they love stabbing people when they’re down. The weapons are also used in hooking jabs attacks, which deal damage and grab on a hit, and on non-damaging unbalancing thrusts (minor actions) which target a grabbed creature and knock them prone on a hit.
Their tactics are obvious from the ability descriptions: Hooking Jab; Unbalancing Thrust; stabstabstabstab. Send your beefy defenders to fight them, because Unbalancing Thrust targets Fortitude.
Our spellcasters, or more precisely psions. They preserve the old lore that gave the original derro access to the Far Realm, and spend their time deep inside the ruins of their empire trying to find ways to reopen the old portals. They wield scourges in combat, and use orbs as their implements.
Savants are Level 16 Controllers with 154 HP. They have a ground speed of 5 and a teleport speed of 3. Their scourges damage and inflict a -2 attack penalty for a turn. Their basic ranged attack is Mind Scourge, which deals psychic damage and forces the target to choose between taking 10 ongoing psychic damage or being dazed. The chosen condition is (save ends) either way.
The savant can also open a mini-portal to the Far Realm with the Window to Madness power. This creates a small zone (area burst 1) centered on an ally within 10 squares. The zone lasts until the end of the encounter, and any non-derro that enter the zone or ends their turn there take 10 psychic damage. The savant can end the zone early with a minor action, in which case the power recharges. It can also slide every creature inside the zone 2 squares as a minor action.
This is not a derro, but a slave that was subject to their experiments and warped into a tentacled abomination. The stats could also be used for a generic Thing From Beyond summoned from a derro portal or other Far Realm opening.
These unfortunates are Large Aberrant Humanoids and Level 16 Brutes with 193 HP. They have Speed 6 but can’t shift, and they have Darkvision.
The warped slave’s Disintegrating Mind works as an aura (1), which deals psychic damage to enemies caught inside. If a derro inside the aura uses its Strength of Madness ability, the slave gets to make a free tentacle attack.
This thing can Bite or use Tentacles to fight. The tentacles grab and pull the target 1 square in addition to dealing damage. When bloodied, it gets desperate and gains a Flailing Tentacles attack that affects all enemies in a Close Burst 2, damaging and pulling them 1 square on a hit.
Warped Slaves follow the orders of their derro masters, or rampage about the battlefield trying to attack the nearest enemies. It often amounts to the same thing.
The whole “Shaver Mysteries” horrific underground humanoid vibe is quite evocative, and judged on that merit alone I’d rate the derro very highly as RPG monsters. However, in the context of D&D they end up being just one more species of evil Underdark dwellers who like slavery and torture, this time in size Small. If I include derro in a game, I’m probably removing at least one of the others, and maybe more.
Mechanically they’re okay, and you have enough here to make a whole derro-themed dungeon. For spice, you could add aboleth leaders and mind flayer allies.