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

Multiple Heads. The hydra has five heads. Each head has one of the following attributes: acid damage (black dragon head), lightning damage (blue dragon head), poison damage (green dragon head), fire damage (red dragon head), or cold damage (white dragon head). 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. 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 or breath attacks as it has heads.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 10 (1d10 + 5) piercing damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.

Frightful Presence. Each creature of the hydra's choice that is within 120 feet of the hydra and aware of it must succeed on a DC 16 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 hydra's Frightful Presence for the next 24 hours.

Draconic Breath (Recharge 5–6). The hydra exhales substance of the chosen type in a 60-­foot line that is 5 feet wide. Each creature in that line must make a DC 18 Dexterity saving throw, taking 54 (12d8) of the chosen damage on a failed save, or half as much damage on a successful one.

Amphibious. The hydra can breathe air and water.

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

Cannibalic Sacrifice: Once per combat, the hydra can devour one of it's own head to regrow three of it's heads that have perished and restore 75 hit points. These heads will have the attributes of the perished heads.