Your Charisma and Wisdom increase by two and your Constitution increases by one.

Aquan Tieflings age slower than most and they look younger than they are. They have large lifespans living anywhere from 200 to 300 years.

While there has been lawful or neutral aligned most Aquan Tieflings are chaotic aligned.

Aquan Tieflings Size can vary depending on the creature they resemble and can be any size however most are usually medium.

Aquan Tieflings can vary in speed however most Aquan Tieflings have a walking speed of 30ft and a swim speed of 60 ft.

Aquan Tieflings don't rely on their eyes and have become blind. However, they have learned other methods of sight and now have Blindsight in a 120ft radius. 

Aquan Tieflings can live almost anywhere in the sea including the deepest depths. This not only lets them ignore the drawbacks but also they resist the cold and force from attacks and just in general. They are also obviously amphibious and can breathe air and water. Finally living in the sea has given them an understanding of sea life allowing them to convey simple ideas to them.

Their infernal legacy has changed to better suit where they live and have learned new spells; At 1st level, you learn Ray of Frost cantrip to cast at will. Starting at 3rd level, you can cast Ice Knife with it. Once you cast a spell with this trait, you can’t cast that spell with it again until you finish a long rest. Charisma is your spellcasting ability for these spells.

These Tieflings have no need to know infernal down in the sea and instead learned to speak, write, and understand Aquan and Primordial.