The Lernaean hydra

Version 0.30: This article may not be up to date for the latest stable release of Crawl.

the Lernaean hydra D
HP	99-200
HD	30
XP	5262
Speed	10 (swim: 60%)
AC	0
EV	5
Will	120
Attack1	18 (bite: plain)
Resistances	rPois+ rDrown
Vulnerabilities	None
Habitat	Amphibious
Intelligence	Animal
Uses	Uses nothing
Holiness	Natural
Size	Giant
Type	hydra, hydra
Flags	Cold-blooded Regenerates Unique

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 that appears in one of the branch endings of the Swamp. 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, can knock down trees by simply moving through them, swims as fast as any hydra, and regenerates quickly.

Strategy

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 high Armour skill and highly enchanted armour can expect to take at most 20-30 damage/turn from this monster. Not trivial, but manageable.
• 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.

Weaknesses

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.
• 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

• Flaming edged weapons still cut off heads as usual, though having 27 heads makes this less noticeable. It may help in taking out Lerny slowly, provided you have renewable or cheap methods of escape.
• Considering Lerny is already maxed out at 27 heads, the only negative effect of attacking with an edged weapon is the health it regains when regrowing any heads you cut off. You probably won't be able to kill it with an edged weapon before it eats you, but a weapon of freezing might slow it down long enough for you to get some distance.
• A phantom mirror could help vanquish Lerny or greatly reduce its health. Could is the keyword here, as either hydra copy could easily maul the other, first.
• 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 or undead, who are also affected by immolation.

Trivia

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