Fiendish Vigor 5e vs. Armor Of Shadows dnd
Fiendish Vigor 5e has so many more benefits than Armor of Shadows. In d&d 5e, it protects against all damage and not just attack rolls. It will also help you avoid getting hit often in the backline. It allows you to exit combat with your temp hp absorbing the hit. That is more common if you have temp hp from other sources, such as if your character is a fiendlock. It was helpful for all levels of archfey warlocks through OotA. Get studded leather.
Fiendish Vigor, an eldritch invocation, is available in the 5th edition.
As a 1st-level magick, you can make false life for yourself without having to expend any spell slots or material components.
The OGL publishes the material from the 5th Edition SRD.
ARMOR OF SHADOWS 5E
You may cast mage armor on yourself at will, without employing a spell slot or material components. You will find it in DnD 5e Eldritch Invocations at Player’s Handbook.
Fiendish Vigor can be helpful to level 3. At that point, I would trade it for the armor of shadows or Armor of Agathis. The second-level spell slot would grant ten temp HP instead of the usual 8.
Fiendish Vigor lets you cast False Live at will to gain 1d4+4 temporary hit points. It can be cast at will and lasts for 1 hour. You could repeat it until you get a 4. It can be done out of combat every 6 seconds. Your eight temporary hitpoints will be available to you before the battle.
Do I assume that a Warlock equipped with the 5e Fiendish Vigor Invocation begins every combat with eight temporary HP?
It’s not impossible. If the player is willing to agree, you can assume that a warlock equipped with that invocation begins with their buffs.
In a 3.5 game, all the players were highly optimized and self-buffing characters that would stack buffs against themselves before each combat. Everyone was too busy to announce their buffs at every encounter. The DM assumed we all had them on at the beginning of each encounter. We then subtracted the resources. This system was flawless.
Keep that in mind. Having a spell constantly means they will be detected by detect magic. There might also be instances where you might attract unwanted attention.