They are immune to any and all types of fire, and cannot get hurt by it in any way.

they can use these spells, having fire magic.

When water touches them, like rain, it burns their skin. It isn't major pain and doesn't cause much damage, healing pretty quickly, but they do sting and cause minor burns wherever it touches. they take -1 damage whenever it rains directly on them or through leather or cloth armor/clothes. they take -3 when swimming or getting covered/submerged with/in water, unless wearing/using the proper things to protect them from it. (any kind of water resistance potions, water-proof armor, etc.)

Your Intelligence score increases by 1, and your Charisma score increases by 2.

Tieflings mature at the same rate as humans but live a few years longer.

Tieflings might not have an innate tendency toward evil, but many of them end up there. Evil or not, an independent nature inclines many tieflings toward a chaotic alignment.

Tieflings are about the same size and build as humans. Your size is Medium.

Your base walking speed is 30 feet.

You know the thaumaturgy cantrip. When you reach 3rd level, you can cast the hellish rebuke spell as a 2nd-level spell once with this trait and regain the ability to do so when you finish a long rest. When you reach 5th level, you can cast the darkness spell once with this trait and regain the ability to do so when you finish a long rest. Charisma is your spellcasting ability for these spells.

You can speak, read, and write Common and Infernal.