Blood Moon Hydra

Lunar Blood. When the Blood Moon Hydra takes piercing or slashing damage, each creature within 5 feet of the Blood Moon Hydra takes 18 (5d6) radiant damage.

Hold Breath. Blood Moon Hydra can hold its breath for 1 hour.

Legendary Resistance (5/Day). If the Blood Moon Hydra fails a saving throw, it can choose to succeed instead.

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

Whenever the Blood Moon Hydra takes 40 or more damage in a single turn, one of its heads dies. If all its heads die, the Blood Moon 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 60 or more fire damage since its last turn. The Blood Moon Hydra regains 30 hit points for each head regrown in this way.

Reactive Heads. For each head the Blood Moon Hydra has beyond one, it gets an extra reaction that can be used only to make opportunity attacks.

Siege Monster. The Blood Moon Hydra deals double damage to objects and structures.

Wakeful. While the Blood Moon Hydra sleeps, at least one of its heads is awake.

Hydra's Growth (Mythic Trait; Recharges after a Short or Long Rest). If the Blood Moon Hydra is reduced to 0 hit points, it doesn't die or fall unconscious. Instead, it regains 375 hit points and gains a number of heads equal to the number of heads it has minus five. If it has less than four heads, its number of heads becomes five.

Multiattack. The Blood Moon Hydra makes as many bite attacks as it has heads.

Bite. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 23 (2d12 + 10) piercing damage.

Stomp. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 28 (4d8 + 10) bludgeoning damage.

Tail. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 38 (5d10 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 27 Strength saving throw or be pushed up to 20 feet away from the Hydra.

The Blood Moon Hydra can take 4 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 Blood Moon Hydra regains spent legendary actions at the start of its turn.

Detect. The Blood Moon Hydra makes a Wisdom (Perception) check.

Tail Swipe. The Blood Moon Hydra makes a tail attack.

Trampling Charge (Costs 3 Actions). The Blood Moon Hydra moves up to 50 feet in a straight line and can move through the space of any creature Huge or smaller. The first time it enters each creature’s space during this move, it can make a stomp attack against that creature.

If the Blood Moon Hydra mythic trait is active, it can use the options below as legendary actions for 1 hour after using Hydra's Growth.

Escaping Menace (Costs 3 Actions). The Blood Moon Hydra grows a head and regains 30 hit points. If the Blood Moon Hydra has taken 60 or more fire damage this turn, it doesn't regain the hit points and the head is treated as an undead with immunity to poison and necrotic damage and the poisoned condition and vulnerability to fire damage. Additionally, half of the damage dealt by an undead head with a bite attack, rounded down, is necrotic damage.

Hardened Scales. The Blood Moon Hydra has a +1 bonus to AC until the start of its next turn and regains 20 hit points.

Crimson Roar (Costs 2 Actions). Each creature that can hear The Blood Moon Hydra within 120 feet of it must make a DC 23 Wisdom saving throw. A creature takes 88 (16d10) necrotic damage and is frightened of the Blood Moon Hydra until the end of their next turn on a failed save, or half as much damage on a successful one.