Black dragon snake

supreme ambusher. When the dragon snake attacks a creature that cannot see it, the attack automatically hits and is a critical hit. 

Multiattack. The dragon snake makes a bite attack a tail attack and a claw attack

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 13 (2d6 + 7) acid damage and (2d10) acid damage and if the target is large or smaller   make a DC 17 strength saving thro or be swallowed. The swallowed target cannot breath and is restrained. The dragon worm can have one target swallowed at a time.The dragon worm take one day to digest a swallowed target. If the dragon worm takes 20 damage or more from a creature inside on one turn, it must make a DC 18 con saving throw or regurgitate the swallowed target. If the dragon worm drops to 0 hit points, the swallowed target can spend its action. to escape with a successful DC 18 strength check.

acid spit. RangedWeapon Attack: +8 to hit, range 40/100 ft., 1 target. Hit: 21 (5d8 ) acid damage.

Action Melee Attack. Melee Weapon Attack: +7 to hit, reach 20 ft., 1 target. Hit: 19 (5d4 + 7) bludgeoning damage and the target is grappled(DC18) the dragon snake can have one creature grappled at a time. 

claw. Melee Weapon Attack: +7 to hit, reach #10ft., 10 target. Hit: 13 (1d10 + 7) slashing damage. 

Acid breath. The dragon snake blasts acid in a ___ foot long 5 feet wide line. Each creature in the line must make a DC 18 saving throw or take 54(12d8) acid damage, or half as much on a success.

Tail trap. The dragon snake makes one tail attack on a creature that walks directly below it,  it then makes an acid spit attack on the creature.