Mancer

At 1st level, you can cause a magical eruption of a damage type of your choosing when cast spells.

At 6th level, you gain resistance to the damage type, ignore resistance to the type on enemies, gain a little extra damage, and can change the damage type of other spells to your chosen type.

At 14th level, you can deal damage back to an attacker when struck.

At 18th level, you gain immunity to your chosen type and can treat immunity to your chosen type as resistance, so you always get some damage.

Heart of Mancing

At 1st level, choose one of the following damage types: acid, cold, fire, force, lightning, necrotic, poison, psychic, radiant, and thunder, you may change your chosen type when level up in sorcerer.
Whenever you start casting a spell of 1st level or higher that deals damage of your chosen type, magic erupts from you. This eruption causes creatures of your choice that you can see within 5 times your proficiency bonus feet of you to take damage of your chosen type equal to twice the spell’s level.

Energized Veins

At 6th level, you gain resistance to your chosen type. In addition, spells and effects you create that deal your chosen damage type ignore resistance to your chosen damage type and once per turn can deal additional damage equal to your charisma modifier.

Elemental Specialist

At 6th level, when you cast a spell that deals damage that isn’t of your chosen damage type, you can change it to your chosen damage type.

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Elemental Rebuke

At 14th level, when you are hit by a attack, you can use your reaction to deal damage of your chosen type to the attacker. The damage equals your sorcerer level.

Peak of Mancing

At 18th level, you gain immunity to your chosen type. In addition, any spell or effect you create ignores resistance to your chosen type and treats immunity to your chosen type as resistance. Lastly, you may now change your chosen element at the end of a long rest.