Double-Bite. The Xenosaurus has an internal piston like tongue, with an extra set of jaws on it. This drastically increases it's bite power.

Acidic Blood. The Xenosaurus has acidic blood. Any creature within 5 feet of it that lands a melee attack must make a DC 17 Dexterity saving throw or take 3d6 Acid damage. 

Multiattack. The Xenosaurus makes two attacks: one with its double-bite and one with its tail. It can't make both attacks against the same target.

Double-Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 59 (8d12 + 7) piercing damage. If the target is a Medium or smaller creature, it is grappled (escape DC 17). Until this grapple ends, the target is restrained, and the Xenosaurus can't bite another target.

Tail. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 20 (3d8 + 7) bludgeoning damage.

Thunderous Stomp. As a bonus action, the Xenosaurus can stomp it's mighty foot into the ground, causing the land to quake beneath it's weight. Any creature within a 20 foot radius, that is on the ground, must make a DC 15 Dexterity saving throw or be knocked prone. (Recharge 2 rounds)

Acid Spit. As a reaction, when the Xenosaurus is the target for a melee, ranged, or spell attack, it can spit some of it's acidic bodily fluid. The triggering creature must make a DC 17 Dexterity saving throw or take 6d6 Acid damage.