Angler fish

Water Breathing. The Anglerfish can breathe only underwater.

Multiattack. The Anglerfish makes two attacks. one bite attack and 1 tail attack.

Bite. Melee Attack Roll: +11 reach 10 ft. Hit: 22 (3d10 + 7) Piercing damage. The target is grappled (escape dc 17) Until this grapple ends, the target is restrained, and the Anglerfish can't bite another target.

Tail. Melee Attack: +11 to hit, reach 10ft, one target. Hit: 7 (2d12 + 7) bludgeoning damage. 

Legendary Actions Can take 3 Legendary Actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary actions are regained at the start of each turn.

Swallow (costs 2) The Anglerfish makes one bite attack against a large or smaller target it is grappling. If the attack hits, the target is swallowed, and the grapple ends. The swallowed target is blinded and restrained, it has total cover against attacks and other effects outside the Angler fish, and it takes 10 (3d6) acid damage at the start of each of the Anglerfish's turns. The Anglerfish can have only one target swallowed at a time. If the Anglerfish dies or takes more then 40 damage in a round it spits out the swallowed target. the target is spat out. 

Lights out (cost 1): the Anglerfish snuffs out its "Lure" and does a hide action as it prepares to ambush its prey. 

Lure (costs 1): the Anglerfish attempts to lure in a target withing 60 feet. The creature rolls a wisdom save with a dc of 16 or it is Charmed, while charmed in this way the creature must use its Movement and get closer to the Anglerfish. if the target is damaged by any source of damage it snaps out of this effect.