Bogmaw

Amphibious. The bogmaw can breathe air and water.

Mucus Coating. The bogmaw’s skin secretes a sticky mucus. When a creature hits the bogmaw with a melee weapon attack, the attacker must succeed on a DC 13 Strength saving throw or the weapon becomes stuck to the bogmaw. A creature can use its action to make a DC 13 Strength (Athletics) check, freeing the weapon on a success.

Bite. Melee Attack Roll: +6, reach 5 ft., one target.
Hit: 11 (2d6 + 4) Piercing damage, and the target is Grappled (escape DC 13). Until this grapple ends, the target is also Restrained, and the bogmaw can't bite another target.

Swallow. The bogmaw makes one Bite attack against a Medium 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, has total cover against attacks and other effects outside the bogmaw, and takes 10 (3d6) acid damage at the start of each of the bogmaw's turns.

The bogmaw can have only one target swallowed at a time. If the bogmaw dies, a swallowed creature is no longer Restrained by it and can escape from the corpse using 5 feet of movement, exiting prone.

Tongue Lash. The bogmaw lashes its tongue at one Medium or smaller creature within 15 feet. The target must succeed on a DC 13 Strength saving throw or be pulled into an unoccupied space within 5 feet of the bogmaw. If the target is pulled adjacent to the bogmaw, the bogmaw can make a [Tooltip Not Found] attack against it as a bonus action.