Chromatic Hydra

Hold Breath. The hydra can hold its breath for 1 hour.

Multiple Heads. The hydra has five heads. While it has more than one head, the hydra has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Whenever the hydra takes 25 or more damage in a single turn, one of its heads dies. For its chromatic heads, the damage threshold is 30. If all its heads die, the hydra dies.

At the end of its turn, it grows two heads for each of its heads that died since its last turn, unless it has taken fire damage since its last turn. The hydra regains 10 hit points for each head regrown in this way.

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

Wakeful. While the hydra sleeps, at least one of its heads is awake.

Multiattack. The hydra makes as many bite attacks as it has heads. Alternatively, it can use its Spew attacks in place of up to three bite attacks.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 10 (3d6) piercing damage plus 7 (2d6) acid, lightning, or cold damage if the black, blue, or white hydra head respectively made the attack.

Spew Acid. Ranged Spell Attack: +7 to hit, range 120 ft., one target. Hit: 13 (3d8) acid damage and the target's AC is reduced by 1 until the start of the hydra's next turn.

Spew Lightning. Ranged Spell Attack: +5 to hit, range 120 ft., one target. Hit:
13 (3d8) lightning damage. A second creature of your choice suffers half of this damage if they are within 10 feet of the target hit.

Spew Ice. Ranged Spell Attack: +7 to hit, range 120 ft., one target. Hit:  13 (3d8) cold damage and the target's speed is reduced by 10 until the start of the hydra's next turn.

Frightful Presence. Each creature of the hydra's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 14 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.

Can take 3 Legendary Actions, choosing from the options below. Only one legendary Action can be used at a time, and only at the end of another creature's turn. Spent legendary Actions are regained at the start of its next turn.

Detect: The Hydra makes a Wisdom (Perception) check.

Bite Attack. The Hydra makes a bite Attack with one of its chromatic heads.

Breath Weapon (Costs 2 Actions). The Hydra makes one of the following Breath Weapons:

• Acid Breath. The hydra exhales acid in a 60-foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 31 (7d8) acid damage on a failed save, or half as much damage on a successful one.
• Lightning Breath. The hydra lightning in a 60-­foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 31 (7d8) lightning damage on a failed save, or half as much damage on a successful one.
• Ice Breath. The hydra exhales an icy blast in a 60-foot cone. Each creature in that line must make a DC 16 Constitution saving throw, taking 31 (7d8) cold damage on a failed save, or half as much damage on a successful one.