AC 16 (natural armor)
HP 172 (15d12 + 75; bloodied 86)
Speed 30 ft., swim 30 ft.
Proficiency +4; Maneuver DC 17
Skills Perception +5, Stealth +5
Senses darkvision 60 ft., passive Perception 15
Languages —
Hold Breath. The hydra can hold its breath for 1 hour.
Legendary Resistance (3/Day). When the hydra fails a saving throw , it can choose to succeed instead. When it does so, its heads lose coordination. It is rattled until the end of its next turn.
Multiple Heads. While the hydra has more than one head, it has advantage on Perception checks and on saving throws against being blinded , charmed , deafened , frightened , stunned , and knocked unconscious , and it can’t be flanked.
Reactive Heads. For each head it has, the hydra can take one reaction per round, but not more than one per turn.
Regenerating Heads. The hydra has five heads. Whenever the hydra takes 25 or more damage in one turn, one of its heads dies. If all of its heads die, the hydra dies. At the end of its turn, it grows 2 heads for each head that was killed since its last turn, unless it has taken fire damage since its last turn.
Toxic Secretions. Water within 1 mile of the hydra’s lair is poisoned. A creature other than the hydra that is immersed in the water or drinks the water makes a DC 17 Constitution saving throw . On a failure, the creature is poisoned for 24 hours. On a success, the creature is immune to this poison for 24 hours.
Wakeful. When some of the hydra’s heads are asleep , others are awake.
ACTIONS
Multiattack. The hydra bites once with each of its heads.
Bite. Melee Weapon Attack: +9 to hit, reach 15 ft., one target. Hit: 10 (1d10 + 5) piercing damage.
LEGENDARY ACTIONS
The hydra can take 2 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. It regains spent legendary actions at the start of its turn.
Rush. The hydra moves or swims up to half its Speed without provoking opportunity attacks . If this movement would pass through the space of creatures that are not incapacitated or prone , each creature makes a DC 17 Strength saving throw . On a failure, the creature is knocked prone and the hydra can enter its space without treating it as difficult terrain. On a success, the hydra can’t enter the creature’s space, and the hydra’s movement ends. If this movement ends while the hydra is sharing a space with a creature, the creature is pushed to the nearest unoccupied space.
Wrap. Melee Weapon Attack: +9 to hit, reach 10 ft., one Medium or smaller creature. Hit: The target is grappled (escape DC 17) and restrained until this grapple ends. The hydra can grapple one creature for each of its heads. When one of the hydra’s heads is killed while it is grappling a creature, the creature that killed the head can choose one creature to free from the grapple.
Combat
The hydra prefers not to venture more than 30 feet from the water and attacks with surprise if it can. It doesn’t coordinate all its attacks against a single melee opponent if there are several targets available. In melee, it usually uses one legendary action to wrap an opponent and another to rush, escaping with its grappled prey or chasing dangerous ranged attackers. It retreats into deep water if it’s taking excessive damage from ranged attackers it can’t reach.
Legends and Lore
With an Arcana or Nature check, characters can learn the following:
DC 10 Hydras are aggressive, serpent-like creatures with multiple heads. They live in aquatic environments.
DC 15 You can kill a hydra by destroying its heads. But every time one of its heads dies, the hydra grows two more in its place.The only way to prevent a hydra from growing more heads is to cauterize the wound that destroying a head leaves behind.
DC 20 A hydra secretes a toxin that fouls the waters around its lair up to a mile away.
Hydras are aquatic, serpentine creatures with a nasty reputation for being fiercely territorial. Their multiple heads strike lightning fast, allowing them to tear prey limb from limb in seconds. Hydras can survive so long as at least one of their heads lives. For every one of a hydra’s heads that die, two more grow in its place.
Chthonic Guardians Legend has it that only one society has tamed hydras reliably, and that the only reason they have managed to do so is because they are already dead. No one knows why this hidden, underworld civilization has chosen the hydra as its guardian, but many believe that slaying one of these tamed hydras amounts to declaring war upon its undead keepers.
1 Lying in ambush in muddy water
2 Eating a large monster; the hydra’s heads squabble over choice bites
3 Disappearing into water, leaving the half-devoured corpse of a wyvern or giant crocodile
4 Hiding behind rocks or ruined walls
1 A loud splash
2 A distant chorus of roars
3 DC 15 Perception check: muddy tracks
4 Bubbles in the water
Hydras infest swamps and other bodies of water.
CR 5–10 hydra
Treasure 30 pp, 500 gp, 3 pearls (100 gp each), 2 sets of rusted half plate armor, potion of gaseous form , wind fan , ring of water walking
CR 11–16 pyrohydra
Treasure 100 pp, 1,500 gp, 2 sapphires (1,000 gp each), 5 vials of alchemist’s fire, 2 potions of superior healing , necklace of fireballs , ring of protection