Black Doom

I see no, hear no evil, and by my blood, be saved hero.
A dark coloured armour predominantly made out of leather, with small volutes of shadow emanating from it. When it has siphoned some of its user's vitality, it sends forth shadows to protect its intended mark, keeping them from harm.
 
All Torn Down: As an action, you sacrifice some of your health to mend another creature’s injuries. You take 2d4 necrotic damage, which cannot be reduced in any way, and one creature of your choice you can see within 30 feet regains a number of hit points equal to twice the necrotic damage you take. You can use this ability once per long rest.
 
I am all of Me: When you use All Torn Down, you can also spend up to four of your hit dice as part of the action to activate the ability. You restore 2 additional hit points to the target per die expended, and you or the target of All Torn Down (your choice) gain the following.
 
• 2 hit dice: You gain a +1 bonus to your AC for the next minute.
• 3 hit dice: Once within the next minute, you can use your reaction to impose disadvantage on an attack that would target you.
• 4 hit dice: You can teleport up to 20 feet to another point that you can see as a reaction after you have used All Torn Down. You cannot teleport the target you are healing with this ability. You can also suppress one condition affecting you or the target of All Torn Down from the following for 2 rounds: charmed, deafened, frightened, poisoned, restrained. At the end of your turn on the second round, you must make the saving throw associated with the effect (if there is one) again.