Hold Breath. The sailback can hold its breath for 30 minutes.
Multiattack. The sailback makes two attacks: one with its bite and one with its tail.
Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit:21 (3d10 + 5) piercing damage, and the target is grappled (escape DC 16). Until this grapple ends, the target is restrained, and the sailback can't bite another target.
Tail. Melee Weapon Attack: +8 to hit, reach 10 ft., one target not grappled by the sailback. Hit:14 (2d8 + 5) bludgeoning damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or be knocked prone.
Dinosaurs are the dominant form of animal life in Ixalan—the absolute rulers of the coastal lands held by the Sun Empire, and a force to be reckoned with in the interior jungles. A number of dinosaurs appear in the Monster Manual, with even more to be found in Volo's Guide to Monsters, making that a particularly worthwhile resource for an Ixalan campaign. (Many of the dinosaurs in Volo's Guide also appear in Tomb of Annihilation.)