Ancient Evil Dragon

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

Ancient Hatred. The dragon will have increased aggression against any figure resembling a knight.

Dragon's Blood. Once slain, the dragon's corrosive blood flows forth from his wounds, soaking the person nearest to it. The target must make a Strength roll at advantage (DC 17), on a failed check the target will take 27 (6d8) acid damage, or half as much on a successful one. Should the target survive this, it will gain a permanent +2 to its AC against attacks [Physical, Fire, Acid].

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 plus 14 (4d6) fire damage. Target must make a Con save (DC 16), on a failed save, the target takes 1d4 poison damage a turn, and has disadvantage on attack rolls and ability checks. Save can be rerolled on the targets' next turn and lasts until a successful save or 3 of the target's turns

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 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 dragon’s Frightful Presence for the next 24 hours.

Infernal Breath (Recharge 5–6). The dragon 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. Breath attack also leaves a corrosive, burning liquid in the 90-foot cone. Each creature in the area must make a DC 18 Dexterity saving throw, taking 27 (6d8) acid damage on a failed save, or half as much damage on a successful one.

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.