Advanced Dungeons & Dragons 2nd EditionCampaign Setting Logo

Climate/Terrain:Any swampAny marsh, swamp or subterraneanAny marsh, swamp or subterraneanAny arctic or subterranean
Frequency:UncommonVery rareRareVery rare
Activity Cycle:AnyAnyAnyAny
Intelligence:Semi- (2-4)Semi- (2-4)Semi- (2-4)Semi- (2-4)
No. Appearing:1111
Armor Class:5555
Hit Dice:5-125-127-85-8
THAC0:See belowSee belowSee belowSee below
No. of Attacks:5-125-125-85-8
Damage/Attack:See belowSee belowSee belowSee below
Special Attacks:NilExtra headsFireCold
Special Defenses:NilExtra headsNilNil
Magic Resistance:NilNilNilNil
Size:G (30' long)G (30' long)G (30' long)G (30' long)
Morale:Average (8-10)Average (8-10)Average (8-10)Average (8-10)
XP Value:2,0003,0003,0003,000

Hydrae are immense reptilian monsters with multiple heads. For each Hit Die the hydra has, it will have one head. The chart above lists the THAC0 value for hydrae, the number of heads and the damage that they inflict each time they bite.

Hydrae are gray-brown to dark brown, with light yellow or tan underbellies. Their eyes are amber and their teeth are yellow-white. Hydrae have between 5 and 12 heads (1d8 +4).

Combat: Hydrae always have 8 points on each of their Hit Dice and all heads must be severed before the hydra dies. A hydra can bring up to four heads into action against a single foe, biting once with each of them.

Each time a hydra takes 8 points of damage, one of its heads is assumed to have been severed. When this happens, a natural reflex seals the neck arteries shut to prevent blood loss.

Hydrae attack according to the number of heads they have. Therefore, a 10-headed hydra continues to attack as a 10 HD monster even after several heads have been slain.

Attacks on the body have no effect unless a single attack inflicts damage equal to the hydra's original hit points.

Habitat/Society: Hydrae are solitary creatures who prefer dismal surroundings. They gather only to mate.

Ecology: Despite the hydra's size and multiple attacks, they are often preyed upon by dragons. They are impossible to train.

Lernaean Hydra

Although similar to a normal hydra, Lernaean hydrae will regenerate two heads for each one that is severed. A maximum of 12 heads can be grown. New heads form in 1-4 rounds and can be avoided only by the prompt application of flame to the neck following the attack which destroyed the first head. This hydra's body is immune to all attacks.


These reddish hydra have 7 or 8 heads which are able to breathe a jet of fire (5' wide and 2' long) twice per day. This attack does 8 points of damage, halved if a save vs. breath weapon is made.


Each head of this purplish-brown hydra is able to breathe a stream of frost 10 feet wide and 20 feet long which does 8 points of damage. A save vs. breath weapon is allowed for half damage.