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Inspired by: https://www.dndbeyond.com/monsters/1052965-stormhydra

Storm Hydra (10-Headed) CR: 18 (excluding the summons)

Gargantuan elemental, unaligned
Armor Class: 19 (Natural armor plates)
Hit Points: 350 20d20+140
Speed: 40 ft , swim: 30 ft

STR

22 +6

DEX

18 +4

CON

24 +7

INT

10 +0

WIS

10 +0

CHA

5 -3

Saving Throws: STR +11, DEX +9, CON +12, WIS +5
Skills: Skills Athletics +11, Perception +10
Damage Vulnerabilities: Necrotic
Damage Resistances: Thunder, Bludgeoning, Piercing, and Slashing from Nonmagical Attacks
Damage Immunities: Lightning
Condition Immunities: Prone, Frightened, Grappled, Petrified
Senses: Truesight, Passive Perception 20
Languages: Draconic
Challenge Rating: 18 (excluding the summons) ( 21000 XP)
Proficiency Bonus: +5

2/day: Conjure Greater Water/Storm Elemental: Call forth 1 elemental servant. It can be either a Water or Storm Elemental. This elemental will be of Huge size.
The elemental will follow the orders of the Storm Hydra until it is reduced to 0 hit points and disappears.

3/day: Conjure Water/Storm Elementals: Call forth 10 elemental servants. They can be any mix of Water and/or Storm Elementals of regular size.
The elementals will follow the orders of the Storm Hydra until they are reduced to 0 hit points and disappears.


Reflecting Scales: On a successful saving throw against any spell that targets Stormhydra directly is reflected back at a random target.

Multiple Heads. The hydra has 10 heads. While it has more than one head, the hydra has advantage on saving throws against being charmed, blinded, defended, frightened, stunned, and knocked unconscious.
Whenever the hydra takes 30 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 or necrotic damage since its last turn. The hydra regains 20 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.

Actions

Multiattack

The Stormhydra makes as many bite attacks as it has heads, and can then create new heads.

Bite

Melee Weapon Attack: 1d20+12 to hit, reach 10 ft., one target. Hit: 18 2d10+7 piercing damage plus 5 1d10 lightning damage.

Lightning Breath

Each of the stormhydra's heads exhales lighting in a 40-foot line that is 10 feet wide. Each one of these lines originates in a different square adjacent to the hydra, and no line can pass through a space occupied by the hydra.
Each creature in a line must make a DC 19 Dexterity saving throw, taking 44 8d10 lightning damage on a failed save, or half as much damage on a successful one. Creatures affected by the breath of multiple heads must make a saving through for each line they're caught in.

Reactions

Electrified Form. A creature that touches the hydra or hits it with a melee attack while in water and within 5 feet of it takes 5 1d10 lighting damage. In addition, the hydra can enter a hostile creature's space and stop there. The first time it enters a creature's space on a turn, that creature takes 5 1d10 lighting damage and must make succeed a DC 13 Constitution saving throw or become stunned for one round.

Legendary Actions

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 each turn.

Reflected Past. If the Stormhydra fails a saving throw, it can choose to succeed instead. (Legendary Resistances x3)

Swallow. When the Stormhydra makes one bite attack against a Large or smaller target; If the attack hits, the target is also swallowed. A swallowed creature is blinded and restrained, it has total cover against attacks and other effects outside the stormhydra, and it takes 21 6d6 lighting damage at the start of each of the hydra's turns.
If the hydra takes 30 damage or more on a single turn from a creature inside it, the hydra must succeed on a DC 21 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the hydra. If the hydra dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 20 feet of movement, exiting prone.

Thunder Step. 90 feet Instantaneous. You teleport yourself to an unoccupied space you can see within range. Immediately after you disappear, a thunderous boom sounds, and each creature within 10 feet of the space you left must make a Constitution saving throw, taking 3d10 thunder damage on a failed save, or half as much

The Storm Hydra is a massive serpent of surging electricity with a dozen flailing heads. They have reflecting sky blue scales and tracers of pulsing lighting that emanates around the body.
A successful experiment of merging hydra with Air Elementals the Netherese wizards created these beasts to be guardians of their flying cities. Having thought extinct with the fall of the Netherese flying cities a few seems to have survived in the depths of the Eastern Sea. Slowly learning to live under the oceans over the centuries the creatures have become capable swimmers, but are still more adept at moving on land. They have very few enemies under the waves, being one of the largest and most dangerous creatures around.
Draconic was the language used by these mages to train and rear the Storm Hydras, and the hydras retain an understanding of this language.

Suggested Environments

Ocean, Sea, Lakes, Elemental Plane of Water, Elemental Plane of Air


Created by

Komoden.

Statblock Type

Monster

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