Having spend so long immersed in the abyssal waters of the below your body has taken on a number of changes. you gain the following benefits;

• +2 to both constitution and charisma
• Advantage on saving throws against spell effects and death saving throws
• resistance to necrotic damage. 
• you now have the creature type aberration in addition to any other creature types you might have

however, due to your now other worldly nature, you no longer fully benefit from magical healing. As a result half all healing received through magical means (E.G. spells, class features, items), potions are unaffected.