This question came up when discussing the healing effect from the Gloves of Soul Catching. The text for this legendary item states:
After making a successful unarmed strike while wearing these gloves, you can use the gloves to deal an extra 2d10 force damage to the target, and you regain a number of hit points equal to the force damage dealt. Alternatively, instead of regaining hit points in this way, you can choose to gain advantage on one attack roll, ability check, or saving throw you make before the end of your next turn.
So, to put it shortly, you deal force damage to the target of an unarmed strike, then regain health equal to the amount of force damage dealt. But what if that target was yourself?
In any situation, this wouldn't mean much. You would take the force damage and recover this exact same damage. If you had temporary health is where it gets tricky. I have found no rule text or anything else preventing this healing effect from working when damage is dealt to temporary hitpoints, so it seems to me that hitting yourself with the gloves would effectively get rid of your temporary hit points and convert them into "normal" hit points.
Is this reasoning correct, and so can you effectively convert any temporary hit points into actual healing, with no visible downside? Or is there some rule I'm missing that prevents this interaction?
Best Answer
Yes
The gloves deal damage and then heal you for that damage. There is no specification that the target cannot be yourself. The question then becomes whether you can attack yourself with an unarmed strike, and the answer is yes. This is established for example at this answer or if you prefer this tweet by Jeremy Crawford.
The drawback to this method is that you still take the damage from the unarmed strike itself, which deals 1+STR bludgeoning damage and which is not converted into healing. This drawback can be avoided by any character with less than 10 strength, as they don't deal any damage with their unarmed strikes. (Unless hitting for 0 does not count as hitting, which is a whole other question occasionally answered and disagreed on on this site.)
And it gets even better (worse)
By the rules of dnd 5e, you cannot have a negative amount of hitpoints. If you take more damage than your HP (but not so much that you suffer further consequences), your HP is set to 0. This means that a low health character can attack themselves and get to 2d10 hitpoints, which might be higher than what they started with. This process is repeatable and, for a low-strength character, risk-free. Therefore it's possible to arrive at 20 HP for free given some time.
Of course, a DM can disallow it, and indeed likely should if munchkinry goes too far. RAW, however, it works.