
Prerequisite: Must be wearing light, medium, or heavy armor for this to take affect
You have found a way to adjust your armor to enhance specific needs on the battlefield. During every short or long rest you can choose to reduce your AC by 2 to give yourself one of the following benefits until your next short or long rest:
- You gain resistance to piercing, slashing, or bludgeoning damage.
- Your speed is increases by 10ft and you have advantage on initiative rolls.
- You gain a bonus of +1 to attack rolls.
- When you are prone, standing up uses only 5 feet of your movement.
- You have advantage on Dexterity or Strength saving throw.

This feat has no balance to it and should go through some kind of revision. nobody wants a barbarian's to be useless and this feat invalidates both rage and unarmored movement not to mention all the other things like giving you advantage just because you put on a suit of armor.
I don't know, I read it as you get resistance to one of those three damage types (x, y OR z), not all of them (x, y AND z), so it's not as powerful as rage (but I can see how it could be interpreted as resistance to all three)… Plus, you only get the benefit of one of the five things listed, for a cost of 2 AC... Point two could be split into separate points though...
Just as a note, "Prerequisite:" is a condition that needs to be matched in order to take the feat in the first place. Any variable conditions needed to be met (like whether or not you're wearing armour) should be put in the main text bit.
I really like the idea of this feat, but honestly think you could do without the drop to AC, especially since it's only for yourself. Also think you could maybe add "Prerequisite: Proficiency with Tinker's Tools"