Big Mouth Bass

Blood Frenzy. The Bass has advantage on melee attack rolls against any creature that doesn't have all its hit points.

Legs. The Bass uses its hind legs to stand and walk leaving the water.

Water Dependent. The Bass can only be out of water for 1 hour out of 24 hours otherwise it begins to suffocate. After 30 minutes it will begin to die taking 3 d10 damage a round.

Ambusher. In the first round of a combat, the creature has advantage on attack rolls against any creature it surprised.

Rampage. When the creature reduces a creature to 0 hit points with a melee attack on its turn, the Bass can take a bonus action to move up to half its speed and make a bite attack.

Bite. +2 to hit, 12 (2d10 + 1) Piercing damage, 5ft .

Swallow. The Bass makes one bite attack against a Medium or smaller creature it is grappling. If the attack hits, the target takes the bite’s damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the Bass, and it takes 1D4 acid damage at the start of each of the Basses turns.

If the Bass takes 8 damage or more on a single turn from a creature inside it, the Bass must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 5 feet of the Bass. If the Bass dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 5 feet of movement, exiting prone.