Previously I posted some thoughts on the hydra in old school D&D. I’m trying to get it closer to its mythological roots while still keeping it relevant and useable in D&D. The Lernaean Hydra, whose stats are in that previous post, is of course a bit much for all but the highest level and best-prepared characters.
To keep the hydra relevant, as opposed to unapproachable, I suggested that all hydra are a part of the original Lernaean beast and that they are also somewhat mentally linked together.
Here’s a hydra that should interest players in the level 10-15 range. The DM should adjust the number of heads as appropriate.
These stats are basically for Labyrinth Lord, but I include the ascending AC from S&W to be more inclusive. I am also not a fan of treasure class, so I just used what they use for dragons. I would expect there to be a lot of dead bodies with armor, shields, weapons and items scattered about if the hydra is well-known.
No. Encoutnered: 1
Alignment: Chaotic or Chaotic Neutral
Movement: Body 90’ (30’), Heads 120’ (40’) up to maximum length of neck
AC: 3  (heads), 6  (body)
HD: 20 HP/head, 120 for body
Attacks: 1 bite/head (as 12 HD Monster)
Breath 4 times/day as chlorine gas breath weapon
Poisonous gas cloud surrounds the beast at all times
Bite 3-18 + poison (1-6 hp/round until cured)
Breath weapon as dragon—HP of all heads combined as damage, save for half
Poison gas cloud 1-4 hp damage/round save vs. poison for 1-2 half damage
Save: Fighter 10 / Immune to all poisons
Hoard Class: XV
A Great Hydra grows from a severed head of the Lernaean Hydra. It remembers all it knew when it was part of that great beast and especially remembers those responsible for it being cut off. Because it can never again be as great as it once was, these hydrae are extremely vengeful and will, resources permitting, seek out those who separated it from the original and exact vengeance for generations to come.
The heads of a Greater Hydra may be attacked separately. When they are severed or bashed off the neck, two heads of equal hit dice and hit points will grow back on that neck in two rounds (able to act on the third round following). This can be prevented by applying fire or acid to the stump of the neck.
The intelligence of these hydrae vary as they most sustain various amounts of damage when they are beheaded from the Lernaean Hydra. Some of these have bodies shaped for walking, others slither or even have fins for swimming. A greater Hydra’s blood is a powerful poison if ingested or introduced to the blood stream. Any such contact will cause 1-8 HP damage immediately. When distilled and placed on a weapon, it can cause an extra 2-24 HP damage.
An older Great Hydra will often have a number of Lesser Hydrae living nearby. These smaller versions are created when someone severs a head from a Great Hydra. The heads attempt to escape when severed and within a matter of weeks, have morphed into the body and 1-4 heads of Lesser Hydra. In some cases, the larger beast will lure challengers to it in order to lose a few heads, creating lesser hydrae to do its bidding.
A great hydra can telepathically communicate with intelligent creatures in its presence, regardless of language barriers. A Great Hydra needs a great deal of food.