If you do additional necrotic damage from other effects, do you get boosted healing from a Blood Fury Tattoo?

Question

I'm having a bit of trouble wrapping my head around the specific wording in the Blood Fury Tattoo's initial charge burning ability.

When you hit a creature with a weapon attack, you can expend a charge to deal an extra 4d6 necrotic damage to the target, and you regain a number of hit points equal to the necrotic damage dealt.

The only hang-up I have is if I were to have an additional effect, such as Hex, that would add necrotic damage to the attack before the charge's additional effect is used.

You place a curse on a creature that you can see within range. Until the spell ends, you deal an extra 1d6 necrotic damage to the target whenever you hit it with an attack. Also, choose one ability when you cast the spell. The target has disadvantage on ability checks made with the chosen ability.

The way I see it, there's two interpretations, either you gain HP based solely on the extra 4d6 added by the charge, which I think is the knee-jerk reaction to reading this, but alternatively, this could instead be read you regain HP equal to the necrotic damage done by the attack. What do y'all think?

Answer 1

You likely gain from both, but you'll need DM sign off

The wording states:

When you hit a creature with a weapon attack, you can expend a charge to deal an extra 4d6 necrotic damage to the target, and you regain a number of hit points equal to the necrotic damage dealt.

This is almost the same as Vampiric Touch:

The touch of your shadow-wreathed hand can siphon life force from others to heal your wounds. Make a melee spell attack against a creature within your reach. On a hit, the target takes 3d6 necrotic damage, and you regain hit points equal to half the amount of necrotic damage dealt. Until the spell ends, you can make the attack again on each of your turns as an action.

There is another question that deals with Vampiric Touch, and has an accepted answer where multiple sources combine. It also includes a quote from Mike Mearls. And while his responses are no longer considered law, they generally reflect intent.

Answer 2

You heal from both, but ask your DM

The text says:

When you hit a creature with a weapon attack, you can expend a charge to deal an extra 4d6 necrotic damage to the target, and you regain a number of hit points equal to the necrotic damage dealt.

• Did you hit the creature with a weapon attack? Yes.
• Did you deal necrotic damage? Yes, 5d6 in total.

Both these conditions are fulfilled. So you should regain 5d6 hit points, equal to the necrotic damage dealt.

It is not clear that the clause starting with "and you regain" is referring to only the 4d6 necrotic damage. To achieve this, the wording could have been "to deal an extra 4d6 necrotic damage and regain an equal number of hit points."

But, it is also not clear it is not referring to the 4d6, and there are timing rules that can suggest it should, and that create a downside associated with this more generous reading, due to the rule for resolving Simultaneous Effects, found in XtgE, p. 77:

If two or more things happen at the same time on a character or monster’s turn, the person at the game table — whether player or DM — who controls that creature decides the order in which those things happen.

Three effects need to be resolved here, as they happen simultaneously when you hit: expending a charge to deal necrotic damage, dealing necrotic damage from hex, and regaining hit points. If the healing is not coupled to the 4d6 necrotic damage, then it must be independent. This means that if the attack were an opportunity attack on another creature's turn, that creature's player could stack the order to be 1) regain hit points equal to necrotic damage dealt (0 at that point), 2) deal 4d6 necrotic, 3) deal 1d6 necrotic. You would not heal anything.

That seems to be a nonsensical outcome. I therefore think this is not fully conclusive, and the DM might rule with justification that the healing only applies to the tattoo's necrotic damage. Like with any question where you cannot clearly demonstrate it must be one or the other reading, the final word is with the DM.