Un'goro Hydra

Adaptation. The flora and fauna of Un'Goro are ever-changing and constantly adapting. If a property or action causes a creature to adapt, roll a d10 to determine which adaptation the creature acquires, depending on the number rolled. If the creature already has the rolled adaptation, roll a d10 until an adaptation the creature does not yet possess is rolled. The adaptation effect lasts until the creature finishes a long rest.

1. Elemental Protection. The creature gains immunity to damage from sound, acid, fire, cold, and electricity.
2. Resilient Organism. The creature gains immunity to damage from necrotic, poison, acid, and radiation.
3. Psychic Barrier. The creature gains immunity to damage from force or psychic attacks.
4. Durable Carapace. The creature gains immunity to non-magical piercing, bludgeoning, and slashing damage.
5. Sharp Fangs. Each time the creature hits with an attack that deals bludgeoning, slashing, or piercing damage, it deals an additional 2d6 damage of the same type.
6. Maneuverability. The creature gains a flying, swimming, and climbing speed equal to its normal speed (if the creature already has one of these speeds, it remains unchanged).
7. Camouflage. The creature makes Dexterity (Stealth) checks with advantage, and once per day can apply an effect that grants it invisibility, silent movement, and leaves no tracks for one minute.
8. Pounce/Bounce. The creature gains the ability to teleport up to 30 feet to an unoccupied space it can see as a bonus action.
9. Elemental Essence. As a reaction, when the creature takes damage from sound, acid, fire, cold, or electricity, it can gain resistance to that type of damage until the end of the round. Additionally, when the creature first hits with a melee attack on its next turn, the target takes an additional 1d6 damage of the same type.
10. Sharp Spikes. Each time the creature takes damage from a melee attack, the attacking creature takes 1d4 piercing damage.

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

Multiple Heads. The Un'goro 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. 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 and also adapts, for each died head, unless it has taken fire damage since its last turn. The Un'goro hydra regains 10 hit points for each head regrown in this way.

Pinnacle of Evolution. Each time the Un'goro Hydra receives all 10 adaptations, it loses all its current adaptations in order to double the number of its heads. The Un'goro Hydra regains 10 hit points for each head regrown in this way.

Reactive Heads. For each head the Un'goro 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.

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