Gain 2 to primary ability score, and 1 to secondary ability score 

You have darkvision for 60 ft. Magical darkness does not impede your darkvision 

You have advantage on saving throws against spells and other magical effects

Melee classes gain immunity to fire and poison damage, casters gain the following: You know the fire bolt cantrip. [3rd] You can cast hellish rebuke (2nd) once per long rest. [5th] You can cast darkness once per long rest. CHA is your spellcasting ability

You can speak, read, and write Common, Infernal and one language of your choice.

Chosen stop aging when they are chosen, and have never been observed to die of old age.

All Chosen fall to Evil eventually. Each day you are not Evil as a Chosen, at dawn make a DC 17 WIS saving throw. If you succeed, your alignment stays the same. If you fail, your alignment is irrevocably changed to Evil. This cannot be undone unless a Wish spell is cast or you draw the Balance card from a Deck of Many Things.

Chosen come in many shapes and sizes. Generally, Chosen are medium but this is not true for all Chosen. Work with your DM to determine what best fits your character, their task, and their story. 

Your base walking speed is 30 feet.

You are resistant to fire and poison damage.