Catfish

Shapechanger. The catfish can use its action to polymorph into a Small or Medium humanoid it has seen, or back into its true form. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies. While on land, this form can only be maintained for up to 8 hours before the catfish must revert back to their original form and return to the water.

Limited Amphibiousness. The catfish, in their true form, cannot breathe air and must return to the water. If a Catfish takes on the form of a creature that can breathe air, they may breathe air for the duration they are in this form. If a catfish is out of the water in their true form for longer than 30 seconds, they begin suffocating.

From The Mist. While in misty weather conditions, the catfish can channel its innate primal draw to cast misty step 1/day.

Surprise Attack. If the catfish surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 10 (3d6) damage from the attack.

Multiattack. The catfish makes two melee attacks, one with its bite and one with its claws or spear.

Bite. Melee Attack Roll: +4, reach 5 ft. Hit: 5 (1d6 + 2) Piercing damage.

Claws. Melee Attack Roll: +4, reach 5 ft. Hit: 5 (1d4 + 2) Piercing damage.

Spear. Melee or Ranged Weapon Attack: +3 to hit, reach 5 ft. or range 20 ft./60 ft., one target. Hit: 11 (2d6 + 1) piercing damage, or 13 (2d8 + 1) piercing damage if used with two hands to make a melee attack.