Icathian Surprise: Upon being reduced to zero hit points, the Abyssal Mouth will do one final attack as a last ditch effort. It will use its action to dash to the nearest hostile creature, and then explode. The target will need to make a DC 14 Dexterity Save or take 4d6 Acid Damage, half as much on a success

Hawkeye:  This creature does not suffer any penalties from using ranged attacks in melee range

Multi Attack: The Abyssal Mouth can make 4 Living Artillery attacks. It can also substitute two of these attacks for one Caustic Spittle (only one Caustic Spittle per round)

Caustic Spittle: Ranged Weapon Attack: +6 to hit, range 150/600 ft., 1 target. Hit Target is made Vulnerable to all damage from this Abyssal Mouth until the end of the Abyssal Mouth's next turn

Living Artillery Ranged Weapon Attack: +6 to hit, range 150/600 ft., 1 target. Hit: 8 (1d8 + 3) acid damage.