Ancient Red Dracolich

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

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

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

Bite. Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 14 (4d6) fire damage.

Claw. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 17 (2d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +18 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage.

Frightful Presence. Each creature of the dracolich’s choice that is within 120 feet of the dracolich and aware of it must succeed on a DC 21 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 the dracolich’s Frightful Presence for the next 24 hours.

Fire Breath (Recharge 5–6). The dracolich exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 91 (26d6) fire damage on a failed save, or half as much damage on a successful one.

Disrupt Life Breath (Recharge 11-12). The dracolich exhales necrotic gasses in a 90-foot cone. Each creature in that area must make a DC 24 Constitution saving throw, taking 21 (6d6) necrotic damage on a failed save, or half as much damage on a successful one. Any creature who fails the saving throw has disadvantage on Constitution-based saving throws for 1 minute. A creature can repeat the saving throw (at disadvantage) at the end of each of its turns, ending the effect on itself on a success. 

The dracolich 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 dracolich makes a Wisdom (Perception) check.

Tail Attack. The dracolich makes a tail attack.

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