Wardolphin (5e Creature)
From D&D Wiki
Medium beast, neutral
Charge. Swims up to an additional 40ft, if it runs into an enemy more than 20ft away, in slams into it dealing 1d4 + 2 Bludgeoning Damage.
Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 3) piercing damage.
Wardolphins are specially trained to wear customized medium armor. They act on the bidding of their handlers and riders. If their riders are downed or killed they will never leave them be. They will always attempt to recover their body or otherwise protect them.