Demon familiar

A demon is summoned that represents the god to who the cleric is devoted. It has the same hit points as the summoner but without the added constitution. The demon vanishes when it reaches 0HP or is dispelled. Anyone who knows the language of the god can speak to the demon. When the summoner wants to summon the demon, roll wisdom (including modifier). On an 18+ the turtles obeys all commands and is able to perform storm breath twice. On a 15+ the demon obeys all commands and is able to perform storm breath once. On an 8+, the demon must be bargained with, and will obey commands if something is given in return, it is not able to use storm breath. On a 7 or below, roll again without a modifier, if the next roll is below 10 the turtle goes on a rampage and injures the summoner and surrounding people. If above 10 the demon cannot be convinced to do anything but if attacked will retaliate, it cannot use storm breath in either of these cases. 

Turtle demon 

Stats:    13:+1 - Wisdom, 7:-2 Intelligence, 15:+2 - Strength, 15:+2 Dexterity, 13:+1 - Constitution,  3: -4 - Charisma,    Amour: 13 + dex,  Speed: 30ft flying, 40ft swimming. Saving throws: dex, strength. Damage is halved if attacked with water. Languages: Celestial (Turtle god). 

Beak. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) piercing damage. Steam Breath The turtle exhales scalding steam in a 20-foot cone. Each creature in that area must make a DC 16 Constitution saving throw, taking 1d12+3 fire damage on a failed save, or half as much damage on a successful one. Being underwater doesn't grant resistance against this damage.