Innate Spellcasting. Orcus's spellcasting ability is Charisma (spell save DC 24, +16 to hit with spell attacks). He can innately cast the following spells, requiring no material components:
Legendary Resistance (4/Day). If Orcus fails a saving throw, he can choose to succeed instead. Demonic Awakening (Recharges after a Short or Long Rest). If Orcus would be reduced to 0 hit points, his current hit point total instead resets to 367 (80% of his maximum hit points) hit points, he regains any expended uses of Legendary Resistance and he can use 2 more legendary actions per round. Additionally, he can now use the options in the "Mythic Actions" section for 1 hour. Magic Resistance. Orcus has advantage on saving throws against spells and other magical effects. Magic Weapons. Orcus's weapon attacks are magical. Master of Undeath. When Orcus casts animate dead or create undead, he chooses the level at which the spell is cast, and the creatures created by the spells remain under his control indefinitely. Additionally, he can cast create undead even when it isn't night. Wand of Orcus. The wand has 7 charges, and any of its properties that require a saving throw have a save DC of 18. While holding it, Orcus can expend 1 or more of the wand's charges to cast one of the following spells from it: circle of death (1 charge), finger of death (1 charge), or power word kill (2 charges). The wand regains 1d4 + 3 charges daily at dawn. While holding the wand, Orcus can use an action to conjure undead creatures whose combined average hit points don't exceed 500. These undead magically rise up from the ground or otherwise form in unoccupied spaces within 300 feet of Orcus and obey his commands until they are destroyed or until he dismisses them as an action. Once this property of the wand is used, the property can't be used again until the next dawn. Creatures with a challenge rating of 0, as well as plants that aren’t creatures, drop to 0 hit points when within 10 feet of the Wand of Orcus, while attuned to it, all holy water within 10 feet of you is destroyed and animals within 30 feet of you are hostile toward you.
Multiattack. Orcus makes two Wand of Orcus attacks. Wand of Orcus. Melee Weapon Attack: +20 to hit, reach 10 ft., one target. Hit: 21 (3d8 + 8) bludgeoning damage plus 13 (2d12) necrotic damage. Tail. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 21 (3d8 + 8) piercing damage plus 18 (4d8) poison damage.
Pain. Orcus casts power word: pain as a bonus action. Raise. Orcus casts danse macabre as a bonus action with out requiing concentraition, the spell ends when he uses this action again. Bind. Orcus causes skeletal arms to rise from an area on the ground in a 10-foot square that he can see. They last until the end of Orcus's next turn. Each creature in that area when the arms appear must succeed on a DC 24 Strength saving throw or be restrained until the arms disappear or until Orcus releases their grasp (no action required).
Orcus 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. Orcus regains spent legendary actions at the start of his turn. Tail. Orcus makes one tail attack. A Taste of Undeath. Orcus casts chill touch (17th level). Creeping Death (Costs 2 Actions). Orcus chooses a point on the ground that he can see within 100 feet of him. A cylinder of swirling necrotic energy 60 feet tall and with a 10-foot radius rises from that point and lasts until the end of Orcus's next turn. Creatures in that area have vulnerability to necrotic damage.
On Initiative count 20 (losing initiative ties), Orcus can take a lair action to cause one of the following effects; he can't use the same effect two rounds in a row:
Orcus makes his lair in the fortress city of Naratyr, which is on Thanatos, the layer of the Abyss that he rules. Surrounded by a moat fed by the River Styx, Naratyr is an eerily quiet and cold city, its streets often empty for hours at a time. The central castle of bone has interior walls of flesh and carpets made of woven hair. The city contains wandering undead, many of which are engaged in continuous battles with one another.