What are the mechanical implications of a Grave Cleric using a slain ally's essence?

Question

On page 20 of Xanathar's Guide to Everything, the Grave Cleric's Keeper of Souls ability is detailed.

Starting at 17th level, you can seize a trace of vitality from a parting soul and use it to heal the living. When an enemy you can see dies within 60 feet of you, you or one creature of your choice that is within 60 feet of you regains hit points equal to the enemy’s number of Hit Dice

Emphasis mine. I was curious why it specifically outlines slain enemies instead of slain creatures. My initial thought was that without that specific wording you could in theory just keep resurrecting a slain ally by giving him hitpoints back to himself after he died, and that it was written that way to prevent only that case. I do not want to heal an ally with his own essence, but rather a different ally. Rules as written, my judgement says you cannot use a slain ally's essence. But, I want to know if the balance of the game would be significantly upset if one allowed a slain ally's (or non-enemy's) essence to be used on a different ally or oneself. Am I creating any loopholes that could bite me in the butt later? Does healing from any creature's death make the Grave Cleric too powerful or versatile?

Since enemies and allies aren't really defined, I want to be prepared in the event that myself or a player wants to test the bounds of the rules by considering a slain ally as an enemy for the purposes of healing another.

Answer 1

Per the SRD:

A creature that has died can't regain hit points until magic such as the revivify spell has restored it to life.

So you cannot heal a dead comrade by stealing their dead essence.

The above answers the core question, about using a character's own death to resurrect them. The rest seems to be asking for opinion which I thought was frowned upon. But here goes...

No, I don't see a great upset in the balance. This spell is more of a "topping up" heal than granting any great boon. Considering the cleric must be at least 17th level to cast, we can assume that their allies are also 17th level, which means the spell will only heal for 17hp. Whereas at 17th level the cleric has access to the 6th-level spell, Heal:

Choose a creature that you can see within range. A surge of positive energy washes through the creature, causing it to regain 70 hit points. This spell also ends blindness, deafness, and any diseases affecting the target. This spell has no effect on constructs or undead. At Higher Levels. When you cast this spell using a spell slot of 7th level or higher, the amount of healing increases by 10 for each slot level above 6th.

Most other humans the character is likely to meet (and be an ally) would have less than 5 Hit Dice. Which might be enough to bring back another player from the brink of death, but at what cost? Will the cleric kill off a village just to fully heal the party?

The only advantage this has is that instead of one big burst of healing, the cleric can give out a little here and there (depending on how often the cleric is allowed to use the skill per day).

Answer 2

Short Answer: Yes, this would change the balance. But the case of exploiting a player death might be much rarer than an Enemy death...

Enemies are not clearly defined, because the state of a creature can change over the course of an encounter. Spells like Charm Person can change that enemies perception of your character, and then again when the spell's effects are removed. The DM is the ultimate referee for all members of an encounter, and their states of friend, foe, or neutral.

That being said, there are clear rules in class abilities, spells, and other mechanics that clearly define who they affect. In these cases, they statically define who they cover. Allies are usually a fixed characteristic that covers the party and maybe any NPCs that they are confident are continually friendly to them. Enemies turns into a fixed characteristic that can cover all others in most circumstances.

If these applications of their rules were to change, you are making a large change across the board. Consider the Sorcerer's Careful Spell Metamagic, which allows for all allies to get a free save on their Area of Effect spells. Certain spells and effects, in this case your Grave Cleric's "Keeper of Souls" Class Ability, you are only able to affect enemies. Imagine if your abilities that specifically only target enemies now also affect inanimate objects in the area, or some of your damage abilities that spare allies now include them as well...

Also consider that Player Characters handle death differently than NPCs and Enemies. NPCs and Enemies usually "Die" when they hit 0hp. They do not get death saves, nor do they sit at negative hit points. Your players, however, don't automatically die when the reach 0hp or even below, and have a chance to be 'revived', and even have to make death saving throws. Once a player dies though, divine spells are required to bring them back. Considering the average party size is about 4 or 5 players, if you are using this ability on your allies multiple times, you're in way more trouble than you think.

From a DM's perspective, once a single exception is made for such a broad rule in the game, then it opens the flood gates for other players to ask for similar exceptions in their case. Soon, the gaming group will have a laundry list of 'house rules' for very specific cases on spells and abilities.

Your best bet will be to leave the rules for enemy/ally targeting alone because this one single case should happen pretty rarely

Answer 3

Yes it would affect the balance

I don't know specifically about this power, nor do I have any quotes to back this up, but in many computer games there are similar powers and the reasoning is that killing an enemy is an active trigger. You (The group) have to actually do something to get a benefit as opposed to letting it trigger on party death when something is happening to you.

This changes its use from a strict life saver, into something that you have to plan around, and forces you into more active strategies.

Allowing healing from an ally would, imho, change the way the spell is intended to be used. It invalidates to risk vs reward calculation and would make it overpowered.

Healing from any creature would effectively allow you to heal 100% out of combat by killing squirrels, birds and spiders until your party is on full health. That is possibly an even bigger no-no in terms of balance.