Lucifer

AC 24 (natural armor)
HP 290 (20d12+160 ; bloodied 145)
Speed 90 ft., fly 200 ft. (hover)

Proficiency +9; Maneuver DC 27
Saving Throws Con +18, Wis +16, Cha +19
Skills Insight +16 (1d8), Intimidation +19 (1d8), Perception +16 (1d8), Persuasion +19 (1d8), Sleight of Hand +17 (1d8), Stealth +17 (1d8)
Damage Resistances acid, lightning, thunder; bludgeoning, piercing, and slashing from magical weapons
Damage Immunities cold, fire, necrotic, poison; bludgeoning, piercing, and slashing from nonmagical weapons
Condition Immunities charmed , diseased , exhaustion , frightened , poisoned , prone
Senses darkvision 300 ft., truesight 120 ft., passive Perception 30
Languages all, telepathy 300 ft.

Corrupted. Lucifer’s natural and weapon attacks are magical. When he hits with a melee attack, he deals an extra 6d12 necrotic damage (included in the attack).

Infernal Tongue. It is impossible to tell when Lucifer is lying. Additionally, no matter what he says, magic that would determine if Lucifer is telling the truth indicates that he is being truthful, and magic cannot reveal his alignment.

Innate Spellcasting . Lucifer’s spellcasting ability is Charisma (spell save DC 27, +19 to hit with spell attacks). He can innately cast the following spells, requiring no material components:
Constant: detect magic , freedom of movement
At will: animate dead , bestow curse , black tentacles , charm monster , chill touch , create undead , death ward , detect evil and good , disintegrate , dispel evil and good , dispel magic , dominate monster , eyebite ,  greater invisibility , invisibility , finger of death , harm , mass suggestion , plane shift , produce flame , planar ally , suggestion , teleport , vampiric touch , wall of fire
3/day each: gate , incendiary cloud , imprisonment , time stop , weird , wish

King of Darkness. Lucifer can see normally in darkness, both magical and nonmagical.

Lawful Evil. Lucifer radiates a Lawful and Evil aura

Legendary Resistance (3/day). If Lucifer fails a saving throw , he can choose to succeed instead.

Magic Resistance. Lucifer has advantage on saving throws against spells and other magical effects.

Regeneration. Lucifer regains 20 hit points at the start of his turn if he has at least 1 hit point.

Shadow Stealth. While in dim light or darkness , Lucifer can take the Hide action as a bonus action.

Unholy Boon. Lucifer can use his action to touch a creature, granting it infernal power in exchange for something precious to it. For the next 24 hours, each round the creature can roll 1d12 and add it to any ability check , attack roll , or saving throw it makes.

ACTIONS

Multiattack. Lucifer uses his Frightful Presence. He then makes three melee attacks or he uses Soulsucking Touch and makes two melee attacks.

Claw. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 28 (4d8+10) slashing damage plus 39 (6d12) necrotic damage. The target’s hit point maximum is reduced by an amount equal to the necrotic damage taken, and Lucifer regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. If a humanoid is slain in this way, a fiend (with a CR equal to its CR + 3 or its level + 2) rises from the corpse 1 minute later. If a deva , planetar , or solar is slain in this way, a new fallen angel rises from the corpse 1d4 minutes later.

Frightful Presence. Each creature of Lucifer’s choice that is within 300 feet of him and aware of him must succeed on a DC 27 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to Lucifer’s Frightful Presence for the next 24 hours.

Soulsucking Touch. Lucifer reaches out at a creature within 50 feet that he can see, drawing away its life force. The target makes a DC 27 Charisma saving throw or reduces its Intelligence, Wisdom, and Charisma scores by 1d8 (roll separately for each). On a failure by 5 or more, the target rolls d10s instead. The target dies if this reduces an ability score to 0. Otherwise, the reduction lasts until the target finishes a short or long rest . If a humanoid is slain in this way, a fiend (with a CR equal to its CR + 3 or its level +2) rises from the corpse 1 round later. If a deva , planetar , or solar is slain in this way, a new fallen angel rises from the corpse 1 minute later.

Change Shape. Lucifer magically polymorphs into any creature that has a challenge rating no higher than his own, or back into his true form. Lucifer reverts to his true form if he dies. Any equipment he is wearing or carrying is absorbed or borne by the new form (his choice).

In a new form, Lucifer retains his alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, lair actions, and Intelligence, Wisdom, and Charisma scores, as well as this action. His statistics and capabilities are otherwise replaced by those of the new form, including any lair actions of that form.

LEGENDARY ACTIONS

Lucifer 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. He regains spent legendary actions at the start of his turn.
◆ Attack. Lucifer makes a melee attack.
◆ Spell (Costs 2 Actions). Lucifer innately casts a spell.
◆ Conjure Fiend (Costs 3 Actions). Lucifer summons a fiend of challenge rating 15 or lower, which appears in an unoccupied space that he can see within 90 feet. The fiend disappears when it drops to 0 hit points. It obeys any verbal commands that Lucifer issues to it (no action required by him). If he doesn’t issue any commands to the fiend, it acts freely.