Ancient Gold Dracolich

Amphibious. The dragon can breathe air and water.

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Magic Resistance. The dracolich has an advantage on saving throws against spells and other effects.

Turn Immunity. The dracolich is immune to any effect that turns undead.

Spellcasting. The dracolich is a spellcaster, it's spellcasting ability is intelligence(spell save DC 26, +18 to hit with spell attacks). The Dracolich has the following wizard spells:

Cantrips (at will): Chill Touch, Eldritch Blast, Fire Bolt, Infestation, Mind Sliver, Poison Spray, Shocking Grasp, Toll the Dead

1st level (8 slots): Ice Knife, Magic Missle, Ray of Sickness, Sheild, Silvery Barbs, Tasha's Hideous Laughter

2nd level (6 slots): Cloud of Daggers,  Earthbind, Acid Arrow, Wither and Bloom

3rd level (6 slots): Animate Dead, Counterspell, Dispel Magic

4th level (6 slots): Blight, Evard's Black Tentacles

5th level (6 slots): Cloudkill, Negative Energy Flood

6th level (4 slots): Circle of Death, Disintegrate, Summon Fiend

7th level (4 slots): Finger of Death, Power Word Pain, Reverse Gravity, Forcecage

8th level (3 slots): Abi-Dalzim's Horrid Wilting, Power Word Stun

9th level (2 slots): Power Word Kill, Time Stop

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage. When the dragon hits with its bite, the target of the attack suffers disadvantage on weapon attacks until the end of its next turn.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 17 (2d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 24 Wisdom saving throw or become frightened for 1 minute. While a target is frightened by the dracolich's frightful presence it is paralyzed and takes 18 (4d8) psychic damage at the start of each of its turns. 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 the dragon's Frightful Presence for the next 24 hours. 

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons. A humanoid slain by the dracolich's breath weapon rises as a zombie under the dracolich's control. The zombie acts immediately after the dracolich's initiative count in combat.

Fire Breath. The dragon exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 71 (13d10) fire damage on a failed save, or half as much damage on a successful one.

Weakening Breath. The dragon exhales gas in a 90-foot cone. Each creature in that area must succeed on a DC 24 Strength saving throw or have disadvantage on Strength-based attack rolls, Strength checks, and Strength saving throws 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.

Spellcasting. The dracolich is a spellcaster, it's spellcasting ability is intelligence(spell save DC 26, +18 to hit with spell attacks). 

Change Shape. The dragon magically polymorphs into a humanoid or beast that has a challenge rating no higher than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (the dragon's choice).

In a new form, the dragon retains its alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, lair actions, and Intelligence, Wisdom, and Charisma scores, as well as this action. Its statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

Raise the Horde (1/day) . The dracolich creates 10 (2d6 + 3) wights, which rise from the ground in unoccupied spaces of the dracolich's choice within 120 feet of it. The wights act as allies of the dracolich and remain until the dracolich dies or for 24 hours.

Dread Counterspell. The dragon utters a dread word to interrupt a creature he can see that is casting a spell. If the spell is 4th level or lower, it fails and has no effect. If the spell is 5th level or higher, the dragon makes an Intelligence check (DC 10 + the spell's level). On a success, the spell fails and has no effect. Whatever the spell's level, the caster takes 10 (3d6) psychic damage if the spell fails.

Fell Rebuke. In response to being hit by an attack, the dragon utters a fell word, dealing 21 (6d6) necrotic damage to the attacker, and the dragon teleports, along with any equipment he is wearing or carrying, up to 30 feet to an unoccupied space he can see.

Will of Vile Darkness. If the dragon casts a spell that requires concentration but is already concentrating on another spell, he instead has the Book of Vile Darkness concentrate on the spell instead. He can only have the book concentrate on one spell in this way at any time. If the dragon ever needs to make a Constitution saving throw to maintain concentration while concentrating on two spells in this way, he only makes one saving throw to maintain concentration on both spells.

The dragon 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 dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Vile Darkness (Costs 3 Actions). Magical darkness spreads from a point the dracolich chooses within 60 feet of it, filling a 20-foot-radius sphere until the dracolich dismisses it as an action, uses this lair action again, or dies. The darkness spreads around corners. A creature with darkvision can’t see through this darkness, and nonmagical light can’t illuminate it. A creature that enters the darkness or starts its turn in it takes 20 (4d10) necrotic damage.

Death's Grasp (Costs 3 Actions). Skeletal hands reach out of the ground and attempt to grasp up to 7 creatures of the dracolich's choice that are within 120 feet of it. Each creature must succeed on a DC 15 Dexterity saving throw or take 19 (3d12) cold damage and become grappled by the hands (escape DC 15) until the dracolich uses this lair action again or dies.

On initiative count 20 (losing initiative ties), the dragon takes a mythic action to cause one of the following effects; the dragon can’t use the same effect two rounds in a row:

• Activate the Book of Vile Darkness to summon 1d8 Boneless
• Activate the Book of Vile Darkness to summon Zombie Clot once
• Drink from the Abyss gain 10d12 hit points