Primordial Level 1 Transformation Boon: Primordial Affinity (Water)

While able to control all elements, your Primordial birth was sparked by one particular element: your Primordial Affinity. Your body is infused with malleable elemental energy. You must choose an element below and gain all the benefits of that element:
Air. You have resistance to lightning damage. In addition, you can channel the air currents around you to guide a ranged attack. Once on each of your turns, when you make a ranged weapon or ranged spell attack, you can make that attack with advanage. If you are in a location without an air current - such as underwater - this feature has no effect.
Earth. You have resistance to poison damage. In addition, whenever you gain temporary hit points, you gain that many plus your proficiency bonus instead. 
Fire. You have resistance to fire damage. In addition, whenever you deal fire damage, you can add your Constitution modifier to the damage dealt.
Water. You have resistance to cold damage. In addition, whenever a creature regains hit points due to a spell or feature you control, you can imbue them with healing elemental energy. The creature regains additional hit points equal to 1d6 + your Constitution modifier.