Gargantuan construct, neutral

Armor Class 24 (natural armor)
Hit Points 387 (25d20+125)
Speed 100 ft., burrow 100 ft., fly 100 ft. (can hover)

26 (+8) 24 (+7) 20 (+5) 19 (+4) 20 (+5) 10 (+0)

Damage Immunities poison, psychic
Condition Immunities charmed, exhaustion, frightened, paralyzed, petrified, poisoned
Senses darkvision 60 ft., passive Perception 15
Languages tongues, telepathy 100 ft.
Challenge 25 (75,000 XP)


  • Comm. A rendalairn can engage in wireless communications at system-wide range.
  • Juggernaut Resilience. If damage reduces the rendalairn to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is from a critical hit. On a success, the rendalairn drops to 1 hit point instead.
  • Legendary Resistance (3/day). If the rendalairn fails a saving throw, it can choose to succeed instead.
  • Magic Resistance. The rendalairn has advantage on saving throws against spells and other magical effects.
  • Siege Monster. The rendalairn deals double damage to objects and structures.
  • Tongues. A rendalairn understands any spoken language it hears. When it speaks, any creature that knows at least one language and can hear the target understands what it says.


  • Lash. Melee Weapon Attack: +16 to hit, reach 30 ft., one target. Hit: 41 (6d10+8) bludgeoning damage.
  • Disintegration Beam (Recharges 4-6). A beam of energy forming a line 120 feet long and 5 feet wide blasts out from the rendalairn in a direction it chooses. Each creature in the line must make a DC 21 Dexterity saving throw. A creature takes 39 (6d12) force damage on a failed save, or half as much damage on a successful one. If this damage reduces a target to 0 hit points, it is disintegrated. A disintegrated creature and everything it is wearing and carrying, except magic items, are reduced to a pile of fine gray dust. The creature can be restored to life only by means of a true resurrection or a wish spell. This effect automatically disintegrates a Large or smaller nonmagical object or a creation of magical force. If the target is a Huge or larger object or creation of force, this effect disintegrates a 10-foot-cube portion of it. A magic item is unaffected.
  • Juggernaut. Until the beginning of its next turn, the rendalairn has resistance to damage.
  • Quake Pulse (Recharges 4-6). Creatures within 20 feet of the rendalairn must make a DC 21 Dexterity saving throw. On a failed save, a creature takes 19 (3d12) lightning damage and 19 (3d12) thunder damage, becomes prone, and technological devices they are carrying cease functioning until the end of their next turn. A construct becomes incapacitated until the end of its next turn. On a success, a creature takes half damage, does not become prone or incapacitated, and their technology is not affected. Unattended technological devices in the area cease functioning un?l the end of the rendalairn’s next turn.


  • Life Siphon. When a creature within 60 feet of the rendalairn that it can see is reduced to 0 hit points, the rendalairn regains 75 hit points or the creature’s maximum hit points, whichever is less.


The rendalairn can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The rendalairn regains spent legendary actions at the start of its turn.

  • Heal. The redalairn regains 75 hit points.
  • Lash. The rendalairn makes one bite attack.
  • Override. The rendalain targets one construct it can see that is incapacitated. The construct must make a DC 20 Wisdom saving throw. On a failure, the construct is no longer incapacitated, and the rendalairn can issue it commands which the target must obey on its turn. It can specify a simple and general course of action, such as “Attack that creature,” “Run over there,” or “Fetch that object.” If the creature completes the order and doesn’t receive further direction from it, it defends and preserves itself to the best of its ability. The rendalairn cannot give commands that are obviously self-destructive. The target is no longer controlled at the end of its next turn.


Spacefarers sometimes whisper about great cosmic menaces hurtling across the void. According to such reports, these monstrosities are giant metallic spheres traveling in normal space at speeds so fast they preclude engagement. The massive spheres are said to have the ability to sunder asteroids and crack planets, sprouting razor-edged lashes that whirl around them in a lethal flurry. Enough sightings have occurred that authorities are concerned.

The creature’s name, rendalairn, derives from a monster from an old spacefaring tale, but others refer to these creatures as “planet slayers.” There are two accounts of a rendalairn landing on a planet and starting a rampage that ended only when the construct was done destroying everything it could find, including sapient life. The two targeted worlds are home to the ruins of two different technologically advanced but extinct species. Some speculate that rendalairns choose technological societies and sites.

Rendalairn are thought to be solitary. A few scientists have asserted, given the evidence, that “the” rendalairn is unique. Disparities in description, such as coloration or composition, could be attributed to observational errors. Whatever the case, a rendalairn is spherical with a 30-foot diameter. When its lashes extend, the creature can reach up to 60 feet away. From this data, xenobiologists and engineers have speculated the creature weighs at least 50 tons.

Products of advanced scientific technology, the constructs called robots are animated by engineering and advanced science rather than magic. Unlike most constructs, robots are often capable of independent thought rather than being simple automatons. However, they still must obey the programming instilled in them at their creation.

Any robot whose creator hard-coded limitations into its programming can never be truly autonomous.

Robots almost always arise from cultures that possess technology that is leaps and bounds ahead of other civilizations, though sometimes they appear due to cultural diffusion from such a society. A wrecked spacecraft, a portal through time, or a group of robots mass-producing others of their kind could all bring robots into a world. Robots that appear from another place or time might still follow the alien dictates of their original programming, or could run amok, their directives corrupted or forgotten. Whatever the case, these robots possess technology that is beyond the means of almost anyone to reproduce, and they represent a stark contrast to other constructs, as they have nothing to do with magic.

Some spellcasters, despite lacking any real grasp on the technological principles required to create robots, have managed to create their own robots by cobbling together spare parts and broken machines, filling in the gaps and completing the design with a mixture of magic and barely understood fragments of science. These inferior designs usually lack the inexhaustible power supplies, advanced intellects, and self-repair systems found in the original robots, and the magic used in their creation can potentially render them more susceptible to techniques that work against other sorts of constructs.

Robots serve a wide range of purposes, from warfare and defense to peaceful tasks like excavation, farming, and maintenance. Small villages that find robots and somehow manage to command them will often put them to work quietly tending fields or constructing buildings all day long. Armies and warlords collect the more dangerous varieties of robots, but even the more ordinary varieties can be deadly. Most robots sport alloyed skin as hard as steel, meaning that even the lowliest worker robot presents a potent threat when altered for battle.

Furthermore, since most cultures lack a means to reliably repair or understand how to command robots, even the most benign one might malfunction, or even reach a point in its programming where it changes its activity and refuses to follow orders, leading to untold death and destruction among its former temporary masters.

The means of commanding robots vary from model to model, which can be a source of endless frustration for any who seek to control them. Some obey orders from any humanoid, some bond to a specific master until her death, and others only yield to the command of technological brooches or control rods. Still, others submit after mechanical surgery or rebuilding, or not at all. Many must be given extremely precise instructions, for they are unable to process metaphors or other figures of speech, and may interpret them in unanticipated ways, much to the chagrin of those who would command them. A surprisingly large proportion of uncontrolled robots already speak Common, as most models exhibit considerable linguistics talent, and the robots train each other in their new home’s languages. Though they comprehend language, most robots rarely speak save for terse acknowledgments of orders. Their speech typically excludes words they deem unnecessary with their mechanical efficiency, leading to strange, disjointed statements that convey the requisite information without emotion, although some robots programmed to interact well with humans are able to speak in a more fluid and less disconcerting manner.

Constructing a robot requires no magic but does involve advanced and extraordinarily rare materials and technological expertise. Because almost no one possesses the skills and materials to complete the process of constructing a robot, these entries omit the construction sections provided for most constructs. A GM can add the robot subtype to a different type of construct, such as an animated object or homunculus, to create new types of robots. Typically, this doesn’t alter the construct’s challenge rating. A character can’t create a robot from or add the robot subtype to a construct that has already been created; adding the robot subtype to an existing creature is purely a means for the GM to simulate additional robots beyond those provided here.

Section 15: Copyright Notice

Mechanical Monsters (5E) © 2023, Legendary Games; Authors: Jason Nelson, Miguel Colon, Robert J. Grady, Nicholas Hite, Matt Kimmel, Michael Mifsud, James-Levi Cooke, Dan Dillon, Mike Myler, Ismael Alvarez, Jeff Lee, John Lynch.

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