Adult Three-Headed Dragon

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

Multiple Heads. The dragon has three heads of red, blue, and white dragons. While it has more than one head, the dragon has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Reactive Heads. For each head the dragon has beyond one, it gets an extra reaction that can be used only for opportunity attacks.

Magic Resistance. This creature has advantage on saving throws against spells and magical effects.

Multiattack. The dragon can use its Frightful Presence. It then makes three bite attacks. The dragon may instead use two of its breath weapons.

Bite. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 7 (2d6) fire, lightning, or cold damage. The dragon can only deal one of each damage type on its multiattack.

Tail. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 17 (2d8 + 8) 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 20 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.

Breath Weapons (Recharge 6).

Lightning Breath. The dragon exhales lightning in a 90-­foot line that is 5 feet wide. Each creature in that line must make a DC 22 Dexterity saving throw, taking 44 (8d10) lightning damage on a failed save, or half as much damage on a successful one.

Cold Breath. The dragon exhales a frozen wave in a 30-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 36 (8d8) cold damage on a failed save, or half as much damage on a successful one.

Fire Breath . The dragon exhales fire in a 30-foot cone. Each creature in that area must make a DC 22 Dexterity saving throw, taking 42 (12d6) fire 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 10 feet of the dragon must succeed on a DC 23 Dexterity saving throw or take 14 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Breath Weapon (Costs 3 Actions). The Dragon can use one of its breath weapons, but loses one of its reactions until the following turn.