Hel

You are bound by the goddess of the underworld, Hel, who grants you various powers of fire and ice. Followers of Hel take on similar traits being hot-headed one moment and cool and calm the next, which can lead to some interesting situations. To represent your goddess duality, your hair becomes darker or lighter on one side 

Expanded Spell List

The Undying lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Undying Expanded Spells

Spell Level	Spells
1st	burning hands, ray of frost
2nd	scorching ray, Snilloc's Snowball swarm
3rd	fireball, sleet storm
4th	wall of fire, ice storm
5th	immolation, cone of cold

Bonus Cantrips

At 1st level, you learn the produce flame and control flames cantrips.  They count as warlock cantrips for you, but they don't count against your number of cantrips known.

Wrath of Flames

At first level 1, when a creature within 5 feet of you that you can see hits you with an attack, you can use your reaction to cause the creature to make a Dexterity saving throw. The creature takes 2d8 fire damage on a failed saving throw, and half as much on a successful one.

You can use this feature a number of times equal to your Charisma modifier (minimum of once). You regain all expended uses when you finish a long rest.

Unique fire

Starting at 6th level, when you cast fire or cold spells you add your CHA modifier to the damage as Hel lends her strength to you allowing you to deliver a stronger blow 

Flame Within

Starting at 10th level, you gain resistance to fire and cold as you become wreathed in flame for 1 minute.  For the duration all of your attack damage is bolstered by 1d6 fire damage, and you shed bright light for 30 feet and dim light for another 30 feet.  Additionally, any melee attack made against you that you can see takes additional fire damage equal to your Charisma modifier.

Once you use this feature, you can't use it again until you finish a short or long rest.

Hel's Second Chance

The first time you take fatal damage you are instead reduced to 1 HP as you burst in a ball of flame, dealing 6d8 fire damage to everything within a 10 foot radius around you that fails a Dexterity saving throw, and half to those that make the saving throw. 

Once you use this feature, you can’t use it again after a long rest