The Lernaean hydra

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Version 0.31: This article is up to date for the latest stable release of Dungeon Crawl Stone Soup.
the Lernaean hydra DThe Lernaean hydra.png
HP 99-200
HD 30
XP 5262
Speed 10 (swim: 60%)
AC 0
EV 5
Will 120
Attack1 18 (bite: plain)

Resistances rPois+
Vulnerabilities None
Habitat Amphibious
Intelligence Animal
Uses Uses nothing
Holiness Natural
Size Giant
Type hydra, hydra
Flags Cold-blooded
A huge beast, mightiest of hydras, infamous in myth and legend. It flows through the water faster than a human can run, swatting aside trees as though they were matchsticks. Its many heads slaver and gnash constantly as it hunts for prey to slake its bottomless appetite.

“The second Labour which he undertook was the slaying of the Lernaian Hydra,
springing from whose single body were fashioned a hundred necks, each bearing
the head of a serpent. And when one head was cut off, the place where it was
severed put forth two others; for this reason it was considered to be
invincible, and with good reason, since the part of it which was subdued sent
forth a two-fold assistance in its place. Against a thing so difficult to
manage as this Herakles devised an ingenious scheme and commanded Iolaos to
sear with a burning brand the part which had been severed, in order to check
the flow of the blood.”
-Diodorus Siculus, _Bibliotheca Historica_. [4. 11. 5.]. c. 100.

For a list of all reptiles, see list of reptiles and amphibians.

Useful Info

The Lernaean hydra ("Lerny" for short) is a unique hydra with 27 heads. Each head can do up to 18 dmg for a total of 486, though very strongly biased around the average of 260, and reduced 27 times by AC/EV rolls. In addition, it has about twice the HP of a regular hydra, has 30 HD, and can knock down trees by simply moving through them. Other than that, it behaves exactly like a normal hydra (notably that it swims and regenerates quickly).

Lerny can occasionally be found in Swamp:4. If Swamp hasn't generated in your game, it may very rarely appear inside a specific runed door vault ("nicolae_hydra_factorization"). It can also appear as a zombie or skeleton in one ending.


This monster is a threat, and perhaps ranks among the more dangerous monsters in the game. But to a careful, reasonably well-prepared player, it is much less dangerous than it first appears:

  • It presents only a moderate threat to characters with very high AC; AC functions best against many small attacks, and the Lernaean Hydra is just that. A character with 40+ AC (generally from high Armour skill and highly enchanted armour) can expect to take on average 20-30 damage/turn from this monster. By comparison, a character with about 20 AC will take twice as much damage/turn.
  • Low-HP spellcasters who have chosen not to train much in the way of defensive skills should rightfully be afraid. These characters will absolutely want to avoid engaging Lerny in melee, but luckily, they are also the ones best equipped to do so. Use flight to deal with the water, Haste and (careful use of) Swiftness to maintain distance, and repeatedly pelt it with your most powerful attack spells.
    • Lerny's ability to redirect its remaining attacks after a kill means most Summoning spells short of a Malign Gateway will just be mauled down. Even cactus giants aren't effective, as spines only activate once per monster turn. However, summons can still activate Inner Flame/a scroll of immolation.
  • It also presents a threat to characters that are simply low-level. However, you don't have to explore Swamp:4. Unless you're doing a challenge run, you can delay the Swamp rune until after completing Spider:1-3 / Snake:1-3. Note that Lerny doesn't actually show up that often.

Keep in mind that you don't have to kill every monster possible. Sure, Lerny's worth a good chunk of experience, but if you don't have a safe way to kill it, just grab the rune and go. Alternatively, you can come back after you've explored other areas and gotten stronger, since you'll only need the Swamp's rune once you're ready to open the Realm of Zot.


Lerny has several crucial weaknesses that are easily overlooked:

  • It actually has fairly low HP for such a powerful unique, zero AC, and negligible EV. It is also stuck to melee. Ranged attacks can easily wear Lerny down, spellcasters are unlikely to need a source of MP recovery to kill it in one go, and it generally doesn't take long to kill. Even melee characters can use throwing weapons and wands to soften it up before engaging.
  • It has no resistances, other than poison and to throwing nets. Conjurers and elementalists of all stripes will easily be able to inflict damage on it.
  • It cannot see invisible and only has animal intelligence. Not only will Lerny have difficulty tracking you down, but you'll have an easier time dodging attacks and might even be able to get off a devastating stab. Note that being in water without flight will negate most perks of invisibility.

Tips & Tricks

  • A phantom mirror can be brutally effective against Lerny. The phantom often moves first, so it's likely to kill (or severely damage) the original.
  • If there's a suitable mass of monsters of suitable distance, a scroll of immolation will easily vanquish Lerny; preferably with haste, flight, and a ranged attack able to activate a chain reaction. Alternatively, you can set off the reaction with summons, undead, or other allies, who are also affected by immolation.
  • Lerny is a hydra, with the usual head-cutting mechanics:
    • Flaming edged weapons do cut off heads, but going from 27 to 26 heads doesn't make a big difference. If you have a renewable/cheap means of escape, you might be able to chip away at the head count.
    • Lerny is capped at 27 heads. Non-flaming edged weapons still cause the healing, but won't increase the number of heads. While a normal edged weapon will likely prove ineffective, a weapon of freezing can at least slow Lerny down (letting you escape).
    • Lerny is much easier to fight when encountered as a zombie. On top of the usual weaknesses for derived undead, such as lowered speed and willpower, its heads will not regrow when severed, and it will not regenerate health.


The Lernaean Hydra was a monster in Greek mythology that was killed by Hercules as one of his Twelve Labors.