FREQUENCY: Rare

FREQUENCY: Common ([Dungeon Level IX])

FREQUENCY: Rare ([Temperate Civilized Forest], [Temperate Civilized Swamp])
FREQUENCY: Very rare ([Temperate Civilized Mountains])

FREQUENCY: Rare ([Temperate Wilderness Forest], [Temperate Wilderness Swamp])
FREQUENCY: Very rare ([Temperate Wilderness Mountains])

FREQUENCY: Rare ([Tropical Civilized Forest], [Tropical Civilized Swamp])
FREQUENCY: Very rare ([Tropical Civilized Mountains])

FREQUENCY: Rare ([Tropical Wilderness Forest], [Tropical Wilderness Swamp])
FREQUENCY: Very rare ([Tropical Wilderness Mountains])

NO. APPEARING: 1
ARMOR CLASS: 0
MOVE: 12"
HIT DICE: 12 (body)
% IN LAIR: 50%
TREASURE TYPE: [SB]
NO. OF ATTACKS: Up to 10
DAMAGE/ATTACK: 1-6 (x8)/1-12/1-20 ~ 9 <>
SPECIAL ATTACKS: Acid saliva and spitting
SPECIAL DEFENSES: Immune to acid
MAGIC RESISTANCE: Standard
INTELLIGENCE: Low
ALIGNMENT: Neutral
SIZE: L (36' long, 20' tall)
LEVEL/X.P. VALUE: IX | 5800 + 16

SAVES, BODY: 7.8.9.8.10 <+2 save vs. fire if in damp conditions?>

The dreaded thessalhydrae are monsters which love dark && damp conditions, <dreaded: morale modifier?>
so they are typically encountered in swamps, jungles, and subterranean lairs.

Normal attack is from the fringe of snake-like heads which ring the vast
main mouth of the thessalhydra.

Acid Saliva: Each bite inflicts 1-6 points of damage
plus an additional 1-6 unless the victim saves vs. poison.

Spitting: In +addition+, the
main mouth bites for 1-20 points plus another 1-20 points of acid
damage unless a save vs. Poison succeeds. The tail pincer is
used to grasp an opponent, inflict 1-12 points of damage in the process,
and then deposit the victim in the gaping central maw during the same
round.

Each head in the fringe is some 6 feet long, so many creatures can be
attacked during a melee round. Fringe heads each take 12 points of
damage to sever. Thessalhydrae regenerate lost fringe heads in 12 days.
Damage to fringe heads does not harm the body. Once per day a thessalhydra
can spit a glob of acidic saliva from its main mouth. The area
covered is effectively a 12-foot diameter circle up to 3" distant from the
monster. Creatures within this area will sustain 12-72 points of acid
damage and half damage if a saving throw vs. poison is successful.

Immune to Acid: Acids of any sort, including poisonous acids, have no effect upon a thessalhydra.

Note that items placed in the central maw are usually destroyed, as each
owner must savevs. acid and crushing blows every round until the items
are removed.