Caputie

Charge. If the hippocampi moves at least 20 feet straight toward a target and then hits it with a ram attack on the same turn, the target takes an extra 7 (2d6) bludgeoning damage. It the target is a creature, it must succeed on a DC 11 Strength saving throw or be knocked prone.

Water Breathing. The hippocampi can only breathe underwater.  

Aquakinesis. The hippocampi has the ability to control water, including shooting water out of its mouth the way a dragon breathes fire. 

Atmokinesis. The hippocampi has the ability to control water based weather (e.g., snow, rain, hail, etc), but can only maintain the ability as long as they are in the water. They are immune to all water-based weather inside and outside of the water. 

Shapeshifting. The hippocampi can transform into its land form, the horse, at will and immediately upon leaving the water. The sea horse creates a natural water barrier around its nose and mouth upon exiting the water, but has to return to the water within 30 days to reform the respiration bubble. 

Immortality. The hippocampi can never die of old age and is immune to all magic-based attacks.

Enhanced. Strength, speed, senses (jumping and swimming) are all enhanced for the hippocampi depending on its form. 

Ram. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage.

Tidal Wave. Conditional (can only perform in water-based form). Range: 60/120. To Hit: 2d20 + 5. Damage: 3d12 + 7. 5 round charge. 

Water Whip. Uses tail to charge and shape a whip of water. Range: 30/60. To Hit: 1d20 + 5. Damage: 2d6 +3. 

Sea Shield. Given to the hippocampi by Poseidon, when these creatures sense anything unknown to them with an Int level above 0 that does not tangentially align with their alignment, they have the ability to instantaneously create a 60 ft dome of water around self and up to two creatures that are of Good/Neutral alignment. Lasts for up to 1 hour. Requires Concentration for 1 min before being able to attack again.