Fiendish Resilience is a class action unique to 
subclass that lets the Warlock choose a damage type to be resistant to every Short Rest.
Description
Choose a damage type and become Resistant to it. You can pick a new damage type each Short Rest. You can only have 1 type of Resistance at a time.
Properties
- Cost:
-
Action - Details:
-
Recharge: Short rest 
Duration: Permanent
How to learn
Classes:
- Class level 10: Fiend
Notes
- Choices have the form "Fiendish Resilience: <TYPE>", and are: Acid, Cold, Force, Necrotic, Poison, Radiant, Thunder, Bludgeoning, Fire, Lightning, Piercing, Psychic, Slashing