14 (natural armor)
69 (6d12+30)
walk 30 ft., swim 30 ft.
Perception +4
acid
blinded, charmed, deafened, frightened, stunned
darkvision 60 ft.
4
The thessalhydra makes one maw attack and one Flurry of Bites.
Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 7 (1d6 + 4) piercing damage plus 10 (4d4) poison damage.
Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 9 (1d10 + 4) piercing damage plus 5 (1d10) acid damage.
Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 10 (1d12 + 4) slashing damage, and the target is grappled. As an action, the target can escape the grapple by succeeding on a DC 14 Strength (Athletics) or Dexterity (Acrobatics) check (its choice). Until this grapple ends, the thessalhydra can't use its tail pincer.
The thessalhydra spits a glob of acid at a point it can see within 30 feet of it. Each creature within 10 feet of that point must make a DC 15 Dexterity saving throw, taking 18 (4d8) acid damage on a failed save, or half as much damage on a successful one.
The monstrosity can take 2 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. The monstrosity regains spent legendary actions at the start of its turn.
The thessalhydra makes a Wisdom (Perception) check with advantage.
The thessalhydra makes a tail pincer attack.