Allospinus

Aquatic Predator. The Allospinus can hold its breath for up to 30 minutes and has advantage on attack rolls while underwater.

Reckless Predator. At the start of its turn, the Allospinus can choose to attack recklessly. Until the start of its next turn, it has advantage on all melee weapon attack rolls using Strength, but attack rolls against it have advantage.

Multi-Territorial Senses. The Allospinus has advantage on Perception checks based on smell and can detect creatures moving in water up to 120 feet away.

Multiattack. The Allospinus makes three attacks: one with its bite, one with its claw, and one with its tail.

Bite. Melee Attack Roll: +13, reach 10 ft. Hit: 32 (4d10 + 7) Piercing damage. If the target is a large or smaller creature, it must succeed on a DC 18 Strength saving throw or be grappled (escape DC 18).

Claws. Melee Attack Roll: +13, reach 5 ft. Hit: 24 (4d8 + 6) Slashing damage. 

Tail Swipe. Melee Attack Roll: +13, reach 15 ft. Hit: 20 (3d10 + 4) Bludgeoning damage and the target must succeed on a DC 19 Strength saving throw or be knocked prone.

Predator's Charge (Recharge 5–6). The Allospinus moves up to 40 feet in a straight line and can move through Medium or smaller creatures’ spaces. Any creature whose space it moves through must succeed on a DC 18 Dexterity saving throw or take 45 (10d8) bludgeoning damage and be knocked prone.

Terror Roar (1/Day). The Allospinus unleashes a thunderous roar. Each creature of the Allospinus’s choice within 60 feet that can hear it and is not a dinosaur must succeed on a DC 17 Wisdom saving throw or be frightened until the end of the Allospinus's next turn.