Cyberdemon

[JNAProductions]

Cyberdemon
Huge Fiend, Neutral Evil

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Armor Class 22 (Thick Hide)
Hit Points 625 (50d12+300)
Speed 50'

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Strength	Dexterity	Constitution	Intelligence	Wisdom	Charisma
28 (+9)	18 (+4)	22 (+6)	18 (+4)	20 (+5)	22 (+6)

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Saving Throws Strength +15, Intelligence +10
Skills Athletics +21, Arcana +10, Insight +11, Intimidation +12, Perception +11
Damage Resistances Acid, Cold, Force, Necrotic, Psychic, Thunder
Damage Immunities Fire, Poison, non-magical Bludgeoning, Piercing, and Slashing
Condition Immunities Frightened, Exhausted, Charmed, Poisoned
Senses Darkvision 300', Blindsight 60', Truesight 10', Passive Perception 21
Languages Infernal, Abyssal, Common
Challenge X

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Regeneration
The Cyberdemon regains 10 HP at the start of each of its turns, unless it has taken lightning damage since the end of its last turn. The Cyberdemon only dies when it starts its turn with 0 HP and does not regenerate, in addition to failing three death saves.

Conditional Retaliation
When the Cyberdemon suffers from a condition for two consecutive turns, it lashes out. Immediately end all conditions affecting the Cyberdemon, and retaliate based on the conditions cleared.

Blinded
The Cyberdemon's eyes blaze with unholy light, lancing out in searing arcs. Three targets within 30' must make a DC 18 Dexterity save, taking 4d6 fire damage on a failed save, or half on a success.

Deafened
The Cyberdemon lets out a hellish roar. All other creatures within 30' must make a DC 20 Constitution save, taking 2d6 thunder damage and becoming deafened for one minute on a failed save. No damage and not deaf on a successful save. Deafened targets may repeat the save at the end of each of their turns.

Paralyzed
The Cyberdemon draws on its Argent Cell, empowering itself to fight on twice as hard. It immediately spends up to five hit dice, and any attacks it makes until the end of its next turn are considered critical hits.

Petrified
The Cyberdemon's stony prison shatters into high-velocity debris. All other creatures within 30' must make a DC 18 Dexterity save, taking 3d6 piercing damage on a failed save, or half on a success.

Stunned
The Cyberdemon draws a little on its Argent Cell. It immediately spends up to one hit die, and makes its next attack with advantage or imposes disadvantage on the next save it forces anyone to make.

Argent Cell
The Cyberdemon, a horrific combination of hellflesh and technology, is partially powered by an Argent Cell. This generator provides it unparalleled power. While it still possesses it, the Cyberdemon is virtually unkillable. It has the following effects:

-Immunity to lightning damage.
-Regain one hit die at the start of every turn.
-Immunity to the unconscious condition.

Removing the Argent Cell is only possible when the Cyberdemon is at or below 300 HP, leaving the core exposed. Removing it requires either the cooperation of the Cyberdemon (unlikely at best) or forcibly wrenching it out. Doing so involves dealing at least 50 damage in a single turn to the Cyberdemon while able to focus on the core, and wrenching it out with a DC 20 Strength check.

Magical Attacks
The Cyberdemon's attacks are considered magical.

Siege Monster
The Cyberdemon deals double damage to objects and structures.

Actions

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Rocket Ranged Weapon Attack:
Range 600', all targets in a 15' radius circle, DC 18 Dexterity save to avoid damage. Failed Save: 4d6 bludgeoning, piercing, and fire damage. Only halve damage if all three elements are resisted. In addition, the targets are pushed to the edge of the circle by the nearest available route. Successful Save: Half damage and no other effects.

Rush
The Cyberdemon Dashes and performs a single melee attack after ending their move, dealing an extra point of damage for every 5' moved.

Demonic Sword Melee Weapon Attack:
+15 to-hit, reach 15', one target. Hit: 3d10+9 slashing damage, 3d6 fire damage, and 2d8 necrotic damage. The Cyberdemon gains THP equal to the necrotic damage dealt.

Laser Cannon Ranged Weapon Attack:
+10 to-hit, range 1,200', one target. Hit: 6d10 radiant, lightning, and force damage. Only halve damage if all three elements are resisted.

Hell Wave
The Cyberdemon casts Wall Of Fire as a 9th level spell.

Extra Attack III
The Cyberdemon makes four attacks in any combination of Demonic Sword, Laser Cannon, Missile Barrage, or other attack actions.

Bonus Actions

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Berserk
The Cyberdemon incenses itself into a fury until the start of its next turn. It gains resistance to all damage types it doesn't already resist, deals an extra 6 points of damage on all melee attacks, and gains advantage on all attack rolls, but grants advantage to all attack rolls made against it. Using this costs five hit dice.

Calculated
The Cyberdemon takes it cool, calm, and collected until the start of its next turn. It gains +2 to-hit with its ranged attack, and may use the Uncanny Dodge reaction.

Defensive
The Cyberdemon maximizes its defense until the start of its next turn. It immediately Dodges, and gains +2 to its AC. Using this costs four hit dice.

Vengeful
The Cyberdemon sets its sight on those who hurt it until the start of its next turn. It may use Retaliate without expending its reaction. Using this costs two hit dice.

Reactions

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Uncanny Dodge
The Cyberdemon halves damage against a single instance of damage.

Retaliate
The Cyberdemon makes an immediate Missile Barrage, Laser Cannon, or Demonic Sword attack against anyone who damages it.

Rush
The Cyberdemon, in response to being targeted, uses its Rush move.

Legendary Actions

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The Cyberdemon can take three 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 Cyberdemon regains spent legendary actions at the start of their turn.

Attack. The Cyberdemon makes a Missile Barrage, Laser Cannon, or Demonic Sword attack.
Move. The Cyberdemon moves up to its speed.
Rush (Costs two actions). The Cybderdemon uses Rush.

[BerzerkerUnit]

What is the base demon and what setting do the cyber parts come from?

[JNAProductions]

What is the base demon and what setting do the cyber parts come from?

Doom (2016).

[noob]

I prefer the cyberdemon from doom 1993 in part because fighting groups of them is less a chore than fighting monster on which you need to put a finishing move in contact.
Also putting that monster at cr 10 seems a bit dangerous: it means that players are more or less supposed to be able to manage packs of them at high level(part of why I was thinking about the group fighting part)

[JNAProductions]

I prefer the cyberdemon from doom 1993 in part because fighting groups of them is less a chore than fighting monster on which you need to put a finishing move in contact.
Also putting that monster at cr 10 seems a bit dangerous: it means that players are more or less supposed to be able to manage packs of them at high level(part of why I was thinking about the group fighting part)

X is not 10, X is an unknown variable.

Sorry if that's not clear-this beast is WAY more dangerous than CR 10!

[noob]

X is not 10, X is an unknown variable.

Sorry if that's not clear-this beast is WAY more dangerous than CR 10!

Oh so you were not using Roman numerals.
I was already imagining the high optimisation groups you had to fight this with only 4 level 10 adventurers.