If my character has 50 hp, loses 20 hp, and I then cast a 25 thp armor of agathys, what happens if I'm using something like Grim Harvest, Vampiric Touch or Enervation, each of which restore normal hp?
Obviously my pool of normal hp is depleted, do these spells replenish that even if I have a thp buffer on top?
When you have Temporary Hit Points nothing prevents you from healing your actual hit points. The rules for temporary hit points say (emphasis mine):
Healing can't restore temporary hit points, and they can't be added together. [...]
If you have 0 hit points, receiving temporary hit points doesn't restore you to consciousness or stabilize you. They can still absorb damage directed at you while you're in that state, but only true healing can save you.
It is clear from this that healing still functions as normal, otherwise a creature with temporary hitpoints that is unconscious would be unable to be revived.
The rules for Healing handle the normal healing. Note how the temporary hit point rules say nothing to modify your maximum hit points, and that temporary hit points cannot be healed.
When a creature receives healing of any kind, hit points regained are added to its current hit points. A creature's hit points can't exceed its hit point maximum, so any hit points regained in excess of this number are lost.
|, our thp is shown with / and our missing hp is shown with - characters representing 10 points each. If you have 50hp, take 20 damage, then get 20 thp back, your HP bar would look like this: |||--// instead of this |||//. Then if you get healed for 10 HP, it'd look like this: ||||-// and after you are damaged for 10HP while you still have your thp it would change to ||||-/
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Commented
Nov 21, 2019 at 12:26
If temporary hitpoints would prevent healing, it would say so... then he fades, back to being one with the Astral Plane.
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Commented
Nov 21, 2019 at 14:33
The section on "Hit Points" under "Damage and Healing" states:
[...] A creature's current hit points (usually just called hit points) can be any number from the creature's hit point maximum down to 0. This number changes frequently as a creature takes damage or receives healing [...]
And then the section on "Temporary Hit Points" states:
Some spells and special abilities confer temporary hit points to a creature. Temporary hit points aren't actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury [...]
Nowhere in the section does it say that you cannot be healed while having temporary hit points. In fact, they are defined as a buffer against damage, and all of their effects and how they work regarding damage are defined. If they were meant to prevent you from being healed this would be stated. Also note that the section on hit points never states that you are prevented from receiving healing while you have temporary hit points.
Because nothing in the text and rules states or even alludes to temporary hit points preventing you from receiving normal healing, they do not prevent this.
To quote the PHB section on Temporary Hit Points:
Temporary hit points aren’t actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury.
As a result, when you gain Temporary Hit Points, you're not actually healing, and your actual hit points aren't affected. Therefore, when you receive Temporary HP when you're below your maximum HP, you still have whatever damage you've taken to your normal HP, and that damage can be healed normally.
