based on D&D 5th Edition
Huge  Monstrosity , Neutral Evil

Armor Class 17  (natural)
Hit Points 168  (16d12+64)
Speed 50 ft. , swim 25 ft.

23  (+6) 16  (+3) 18  (+4) 7  (-2) 14  (+2) 12  (+1)
Damage Immunities Lightning
Senses darkvision, passive Perception 16
Languages Draconic
Challenge 11  (7200 XP)
Multiattack. make one bite and one constrict attack
Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 22 (3d10 + 6) piercing damage. Target must be grappled then can be swallowed, if size medium or smaller. While inside blinded, restrained, and total cover from outside attacks. Suffers 21 (6d6) acid damage at start of turn. If damage taken by behir is 30 or more on a single turn the behir must make a DC 14 Constitution saving throw or regurgitate swallowed creatures.
Constrict. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 17 (2d10 + 6) bludgeoning damage.
Constrict+. plus 17 (2d10 + 6) slashing damage. target is grappled (escape DC 16), target restrained
Lightning Breath. (Recharge 5-6) Exhales a line of lightning 20 ft. long and 5 ft. wide. Each creature in the line must make a DC 16 deterity saving trhow or take 66 (12d10) lightning damage, half damage on successful save., for 66 (12d10) lightning damage in 20 ft. Line