Is this homebrew feat, Overheal, balanced with regard to other feats?

Question

Is this homebrew feat, Overheal, balanced with regard to other feats?

You have learned to use the healing arts for more than simple recovery post-injury. Now, whenever you use magic to restore one or more hit points to a creature, any healing that would exceed the target's max hp is instead gained as temporary hit points.

The intent is now any excess healing is not wasted but instead turned into temp HP for damage mitigation. For example, say we have a cleric with this feat and a friendly rogue. The rogue is missing 6 HP so the cleric casts Cure Wounds and rolls a lucky 8. This cleric also has a +3 to Wisdom so now normally the rogue would be healed to full and that's it. But with this feat the rogue now also gains 5 temp HP.

Is this significantly more powerful than other feats and/or is it potentially gamebreaking with higher level spells such as Heal being used on a target at full health to give them 70 temp HP?

Answer 1

If I punch my friend in the arm for 1 damage, the feat is easily abused.

This breaks the game with a casting of Mass Heal.

Mass heal:

A flood of healing energy flows from you into injured creatures around you. You restore up to 700 hit points, divided as you choose among any number of creatures that you can see within range.

Cast it, heal myself to 699 temp hp. Balancing Tier 4 encounters is hard enough, but is now impossible when you have a character with 900+ hp, or four characters with 400+ hp.

This feat also turns the spell heal into “Tenser’s tranformation lite” for your friends. Even 70 temporary hp is significant, especially for your high AC tank.

So that covers tiers 3 and 4, where the feat is pretty much broken when used in conjunction with those spells.

Finally, this feat used in conjunction with beacon of hope and cure wounds produces similarly broken effects in tier 1 and 2 play.

Beacon of hope ensures maximum healing, and a 2nd-level cure wounds would be 18-19 temp hp, and just gets better as those spell slots get higher.

I can suggest a solution: cap the temp hp to twice your character level. This scales with your level, and seems more appropriately balanced at each tier of play.

Answer 2

There are some problems. The problems aren't exactly that the ability is too good. The problem is that you're trying to build something to improve in-combat healing, but people who read this are going to see it as a way to do pre-combat buff spells without requiring concentration.

The first problem is that your requirement "whenever you use magic to restore one or more hit points to a creature" is easily gameable. Thomas Markov's answer highlights this issue when he starts with: "If I punch my friend in the arm for 1 damage..." This needs to be replaced with a better requirement that won't get gamed.

The second problem is that you haven't placed a time limit on the temporary hit points. As written, the cleric could overheal each of their allies at the start of the day, and then they just walk around with extra hit points until they need them. (The rules say that, by default, temporary hit points last until you finish a long rest.)

The third problem is that, as you note, certain high-level spells give out very large amounts of healing, and this wasn't seen as a design problem because the people designing those spells expected them just to heal the target to full hit points. You're going to need to add rules to handle this, or else exclude those spells from this ability entirely.

The fourth problem is that the ability is pretty weak, because most spellcasters only use healing on characters that are very damaged, so the risk of hitting someone's hp cap is normally quite low. One fix might be to make this into a "half feat" that also gives +1 stat.

I think the ability you want to design looks like this:

You gain the following benefits:

• When you take this feat, increase your Wisdom or Charisma score by 1, to a maximum of 20.

• Whenever you use a spell of 5th level or lower to restore hit points to a creature, if the creature was damaged by an enemy within the last minute, then any healing that would exceed the target's hit point maximum is instead gained as temporary hit points. The target loses any remaining temporary hit points from this feat after 1 minute.

With this rules text, the ability is no longer viable as a pre-combat buff spell. The spell level restriction excludes heal and mass heal from the effect.