Since my polymorph meme has only garnered three downvotes so far I thought I'd offer a bit more controversial take, and see if I can manage to stir the pot a bit with this one.
So this sent me down an absolute rabbit hole. As a DM there's a few ways I'd consider to stop this being entirely game-breaking:
Personally I would instead depart from RAW and point out a version of option 2, but a lenient one. Something like "you can do this but you are sapping your very essence to do it. Every time you do it, you permanently lose 10% of your HP" or "every time you do this you increase the number of death saving throws you must succeed before you die". Or my personal favourite: "every time you do this you perturb the very laws of nature. Nature is rather fond of its laws and so decides to perturb you right back. Roll on this table to see what happens." and make the table include the above alongside a few other things and maybe a roll on the wild magic table.
In the end I enjoy ingenuity but the role of DM gives you a lot of latitude to... handle... those who believe they found a loophole.
Nature is rather fond of its laws and so decides to perturb you right back.
"Your character has started to understand and unlock the secrets of undeath. Do this again and you may need to find a phylactery quick, because each time moves you one step closer to becoming a lich"
It goes off but doesn't heal you because the text specifically says
The touch of your shadow-wreathed hand can siphon life force from others to heal your wounds.
That's flavour text.
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.
You are, in fact, a creature within your reach.
You're a valid target for the spell, but the heal doesn't trigger cause the target isn't someone other than yourself.
That’s flavour text.
There is no concept of "flavour text" in 5e. If you believe there is, quote a part of the rules that says as such. In 5e, all of the spell description are rules and this has been debated many a times with the very same conclusion.
I mean, there's always a way to houserule something to fix the broken rules. Unless you're DMing an AL game.
Yup, in my experience the best way to beat a rules lawyer is to be a better and funnier rulemaker.
Unfortunately:
As someone who had to DM more than I'd like, no dice, mate.
You're still dealing damage, e.g. it could kill you from the massive damage rule if you dealt enough. Vampiric touch counts how much damage you deal, not how much hp the target loses.
Not to mention I'd allow on creativity and rule of cool. I want players like that in my table.
Okay, if we want to play it like that my ruling as DM is that as all your HP are vampic in nature and you're feeding on the living, you're now undead.
Probably a zombie.
since there is no negative HP you are doing no damage past 0. So even if the spell hits it does no damage since there is no damage left to do, half of 0 is 0.
As I've pointed out in other comments there's a specific rule for damage past 0 HP. It's called “Damage at 0 Hit Points.” under the Death Saving Throws section, and it doesn't say anything about it getting cancelled out.
Having DMed too much. Nope.
This is easily a rule as intended type of thing. If you hit someone else. Sure fine, this is actually awesome and very creative and totally in the spirit of the game.
If you're just trying to break the game. Nope. RPGs aren't about trying to pull apart the systems in place for a group of friends to have fun. Not at our table anyway.
Even the damage dealt thing is silly. Is argue you cant deal damage to something that is fully damaged.
As a DM I don't mind rules-lawyering, but you better be prepared for Consequences later on.
I am a big believer in the rule of cool and as long as everybody is having a good time, I don't mind looking the other way if a player makes a creative interpretation of the rules.
...But you better believe I'm gonna spend some time thinking about what should happen thematically if your wizard starts draining their own death energy to revive themselves.
I like a number of the suggestions here. I think my "solution" here would be to let once slide. The second time, I hand the player a folded note informing them that the toes on their left foot didn't come back with them, causing a visible limp, reduced movement speed and -1 to DEX.
...And we can build from there. Possibly start building a Final Destination style plan.
Cheating Death must have Consequences.
Suggestion: Lich Taint
They haven't become a lich by any means, but they've been touched by the aspect of lichdom. Lich's being rather territorial, they will be noticed by any others with associations to a lich, and that lich will be curious...the player will be investigated. If there is a reason for them to remain curious, expect an interview and serious questions.
RAI you definitely would not be able to target yourself. The spell description starts with: "The touch of your shadow-wreathed hand can siphon force from others to heal your wounds." Technically this sentence is flavor only, but in this case it clearly reveals the intention of the designers.
RAW your meme still works, but I would restrict the spell to target only creatures other than yourself for the reason above. Only if the player has a really cool way to describe how to siphon your own life force and somehow convert it into more life force for yourself, I might allow it...
Not a problem, I’ll just grab some of the years from the end of my life and just kinda stuff them into the present to get me through.
Good as new without any downsid- why is my hair falling out?
This is the reason I only DM barebones frameworks like Mini6. No rules lawyeringˆˆ
Where is the extra HP coming from tho
Vampiric touch counts how much damage you deal, not how much hp the target loses.
It's definitely a flavor fail, but unless you houserule in a cap to damage dealt at 0 hp, (and houserules for how to handle massive damage and the rules for being dealt damage at 0 hp that would be affected,) there's not a limit to how much hp you gain based on the hp of the target.
What about lore-wise?
Seems like you can target yourself but it can only heals "From others".
The failed death save. Kinda. But that's how I would see and rule it.
I’d allow it, but instead of HP damage, you take as many levels of exhaustion.
You trigger after you take damage but before you fall unconscious, like numerous other triggers in the game. I just used the Strength Before Death example because it shows even without magic there's enough time to squeeze a whole ass turn in between those two events.
You trigger after you take damage but before you fall unconscious, like numerous other triggers in the game.
I fail to see how that's supported by RAW. If damage reduces you to 0 hit points and fails to kill you, you fall unconscious.
The fact that a Fighter subclass gives you an ability to act otherwise doesn't affect this, any more than you could say you stay conscious at 0 because Zealot Barbarians can do it. You don't have that ability. You're unconscious or dead when Vampiric Touch triggers. Vampiric Touch fails.
I’d allow it, but instead of HP damage, you take as many levels of exhaustion.
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