Abolethic Vassal.

The skum is permanently charmed by its aboleth master.

Amphibious.

The skum can breathe air and water.

Psychic Conditioning.

The skum is immune to the frightened and charmed conditions unless they are from effects created by an aboleth.

Water Dependency.

The skum takes 6 (1d12) acid damage every 10 minutes it goes without exposure to water.

Actions

Multiattack.

The skum makes three attacks: two with its trident and one with its Mind-Breaking Touch.

Trident.

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) piercing damage.

Mind-Breaking Touch.

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 18 (4d8) psychic damage, and the target has disadvantage on Wisdom saving throws until the end of the skum's next turn.

Skum