Huge monstrosity, unaligned

Actions

Multiattack. The behidra makes as many bite attacks as it has heads, and one constrict attack.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 22 (3d10 + 6) piercing damage.

Constrict. Melee Weapon Attack: +10 to hit, reach 5 ft., one Large or smaller creature. Hit: 17 (2d10 +6) bludgeoning damage plus 17 (2d6 + 6) slashing damage. The target is grappled (escape DC 16) if the behidra isn't already constricting a creature, and the target is restrained until this grapple ends.

Lightning Breath (Recharge 5-6). The behidra exhales a sphere of lightning with a radius that is 20 feet long, centered on the behidra. Each creature in that sphere must make a DC 16 Dexterity saving throw, taking 2d10 (11) lightning damage for each living head the behidra has on a failed save, or half as much damage on a successful one.

Swallow. The behidra makes one bite attack against a Medium or smaller target it is grappling. If the attack hits, the target is also swallowed, and the grapple ends. While swallowed, the target is blinded and restrained, it has total cover against attacks and other effects outside the behidra, and it takes 21 (6d6) acid damage at the start of each of the behidra's turns. A behidra can have only one creature swallowed at a time. If the behidra takes 50 damage or more on a single turn from the swallowed creature, the behidra must succeed on a DC14 Constitution saving throw at the end of that turn or regurgitate the creature, which falls prone in a space within 10 feet of the behidra. If the behidra dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone.