Amphibious. The krolig can breathe air and water.

Magic Resistance. The krolig has advantage on saving throws against spells and other magical effects.

Siege Monster. The krolig deals double damage to objects and structures.

Multiattack. the krolig makes two attacks with its tentacles.  It can also use its tongue or bite.

Tentacle. Melee Weapon Attack: +7 to hit, reach 30 ft., 1 target. Hit: 15 (3d6+3) bludgeoning damage, and the target is grappled (escape DC 12) if it is a Large or smaller creature. Until the grapple ends, the krolig can't use this tentacle on another target. The krolig has six tentacles.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 18 (3d8+3) piercing damage, and the target is swallowed if it is Medium or smaller creature. A swallowed creature is blinded and restrained, has total cover against attacks and other affects outside the krolig, and takes 6 (3d4) acid damage at the start of each of the krolig's turns.  The krolig's gullet can hold up to two medium or four small creatures at one time. If the krolig takes 12 damage or more on a single turn from a creature inside it, the krolig must succeed on a DC 16 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, each of which falls prone in a space within 10 feet of the krolig. If the krolig dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 10 feet of movement, exiting prone. 

Tongue.  The krolig targets one Medium or Smaller creature that it can see within 30 feet of it. The target must make a DC 14 Strength saving throw. On a failed save, the target is pulled into an unoccupied space within 5 feet of the krolig, and the krolig can make a bite attack against it as a bonus action.