Adult Pearlwyrm

Amphibious. The pearlwyrm can breathe air and water.

Deceiving Appearance. When a creature first perceives the pearlwyrm, the pearlwyrm automatically makes a deception check against that creature against it's passive insight. If the pearlwyrm succeeds, the creature views the pearlwyrm as friendly.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 10 (2d6 + 3) slashing damage, and the target must make a DC 18 Athletics or Acrobatics saving throw or be grappled.

Swallow. Melee Weapon Attack: +6 to hit, reach in tile, one target grappled by the pearlwyrm. Hit: 17 (2d10 + 6) bludgeoning damage plus 4 (1d8) acid damage. On a miss, the target takes half damage and can retry the grapple saving throw.

Tail Whip. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Hypnotise. Each creature of the pearlwyrm's choice that is within 40 feet of the pearlwyrm and can see it must succeed on a DC 16 Wisdom saving throw or become charmed for 1 minute. Charmed creatures will attempt to walk towards the pearlwyrm, and if the pearlwyrm targets a charmed creature with any ability, it immediately hits. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to any pearlwyrm's Hypnotise ability.

Regurgitate. The pearlwyrm regurgitates stomach acid in a 30 foot cone. Each creature in that cone must make a DC 18 Dexterity saving throw, taking 28 (6d8) acid damage on a failed save, or half as much damage on a successful one.