Ancient Jade Serpent

Multiattack: The serpent can make two attacks, choosing from the following: Tail attack, bite attack, acid spray, or constrict.

Bite: Melee Weapon Attack: +9 to hit, reach 10 ft. 
Hit: 15 (2d8 + 6) piercing damage and 1d12 poison damage.

• If the target is below 20 hp after being damaged by two successful bite attacks, the target must make a DC 14 Dexterity Save or be swallowed.
• A swallowed creature is blinded and restrained, it has total cover against attacks and other effects outside the snake, and it takes 14 (4d6) acid damage at the start of each of the snake's turns.

Acid Spray: Ranged Weapon Attack: +9 to hit, range 60/120 ft. 
Hit: 16 (3d6 + 6) acid damage.

Tail Whip: Melee Weapon Attack: +9 to hit, reach 20 ft. 
Hit: 22 (3d10 + 6) bludgeoning damage.

Constrict: Following a successful Bite attack, the serpent can use its second attack to wrap and constrict its pray, effectively subjecting the target to the grappled condition.

• Until the grapple ends, the creature is restrained, and the snake can't constrict another target nor use its Tail attack.
• While using this feature movement is halved.
• Only targets size medium and above can be constricted.
• Subsequent turns can be used to constrict the target for another 16 (2d10 + 6) points of bludgeoning damage until it escapes, is killed, or is released.

A creature grappled  by the serpent can use its action to try to escape. To do so, it must succeed on a Strength (Athletics) or Dexterity (Acrobatics) check against the escape DC in the serpent's stat block. If no escape DC is given, assume the DC is 10 + the monster's Strength (Athletics) modifier (DC=19).