Hold Breath. The dolphin can hold its breath for 20 minutes.
Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) bludgeoning damage. If the dolphin moved at least 30 feet straight toward the target immediately before the hit, the target takes an extra 3 (1d6) bludgeoning damage.