Amphibious. The dragon can breathe air and water.

Multiattack. The dragon makes three Rend attacks. It can replace one attack with a Bite attack.

Rend. Melee Attack Roll: +4, reach 10 ft. Hit: 8 (2d6 + 1) Slashing damage.

Bite. Melee Attack Roll: +4, reach 5 ft. Hit: 6 (2d4 + 1) Piercing plus 2 (1d4) Acid damage. If the target is a Large or smaller creature, it has the Grappled condition.

Acid Breath (Recharge 5–6). Dexterity Saving Throw: DC 12, each creature in a 30-foot-long, 5-foot-wide Line. Failure: 24 (7d6) Acid damage. Success: Half damage.

Swallow. Strength Saving Throw: DC 12, one Medium or smaller creature Grappled by the dragon (it can have up to two creatures swallowed at a time). Failure: The target is swallowed, and the Grappled condition ends. A swallowed creature has the Blinded and Restrained conditions and can’t teleport, it has Total Cover against attacks and other effects outside the dragon, and it takes 10 (3d6) Acid damage at the start of each of the dragon's turns.

If the dragon takes 15 damage or more on a single turn from a creature inside it, the dragon must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, each of which falls in a space within 10 feet of the dragon and has the Prone condition. If the dragon dies, any swallowed creature no longer has the Restrained condition and can escape from the corpse using 20 feet of movement, exiting Prone.