I wrote the Spirit and Exorcism domains a few months back, and they got me thinking about domains that imply totally dissimilar approaches to religion and spirituality. Here is another, perhaps more suited to sinister gods, such as the Blood of Vol in Eberron, but gods of battle such as Tempus in FR might find it appropriate. Admittedly, its feature names are more derived from Arioch and Khorne. For me, though, it builds on an idea I had years and years ago, when I was hacking SIFRP to run Birthright: given their emphasis on the right to rule derived from divine bloodlines, it's not impossible to imagine even the most goodly gods of Aebyrnis valuing blood sacrifice.
Some deities, especially those of a more primal or cruel demeanor, hold blood as the essence of holiness. It is the sign of pain, valor, birth, and martyrdom. Some clerics of this domain actively spread violence wherever they go, while others use its power to assure that bloodshed is rare and swiftly ended. Even more than most clerics, those of this domain are forever weighed and tested by their gods, as they choose their own balance between mercy and severity. In many cultures, priesthoods of this domain are pushed into the shadows and the edges of society, becoming mystery cults.
1st: false life, inflict wounds
2nd: enhance ability, protection from poison
3rd: feign death, vampiric touch
4th: compulsion, divination
5th: contagion, greater restoration
Blood for the Gods
At 1st level when you choose this domain, you gain proficiency in all simple and martial weapons that deal piercing or slashing damage, and you gain proficiency in heavy armor.
The Blood is the Life
Also starting at 1st level, you gain temporary hit points equal to twice your cleric level when your current hit points fall below half of your maximum hit points. Once this occurs, it cannot happen again until you complete a short rest.
If your current hit points are below or equal to half your maximum hit points when you roll initiative, you gain temporary hit points equal to twice your cleric level.
Channel Divinity: Bloodgift
Starting at 2nd level, you can use your Channel Divinity to invoke divine favor upon those who bleed and suffer in battle. As an action, you call your deity's name. Up to two allies within 60 feet with current hit points at or below half of their maximum hit points may spend their reactions to make an attack with a piercing or slashing weapon. If these attacks hit, they add your Wisdom bonus to the damage dealt.
At 11th level, this power can affect up to three allies instead of two. At 17th level, this power can affect up to four allies instead of three.
Mighty in Vengeance
Starting at 6th level, when your current hit points are at or below half of your maximum hit points, you may treat any result of 1 or 2 as a 3 on dice rolled to determine damage or healing effects from weapons or spells (not attack rolls or saving throws, but effect values).
Starting at 8th level, once per turn when you make a weapon attack with a piercing or slashing weapon, you deal an additional 1d8 damage of the same type. When you reach 14th level, the damage increases to 2d8.
Further, you add your Wisdom modifier to the damage you deal with any cleric cantrip.
Blood and Souls
Starting at 17th level, when you deal damage that reduces a creature to 0 hit points, you regain an expended use of Channel Divinity, or you regain an expended spell slot. The spell slot's level is equal to half the Challenge Rating of the creature you damaged, or 5, whichever is lower. After you have used this ability twice, you may not do so again until you complete a long rest.
First off, the domain spells: coming up with 4th-level domain spells was especially hard, because 4th level is weirdly thin for several classes. I chose to favor more sinister interpretations of the domain in a lot of cases; if you're playing a more Good-aligned cleric of this domain, think of it as your deity's assurances that no one will ever want to fuck with you.
This will shock everyone present, but I love 4e's Bloodied condition, and I think it was a mistake not to port it as-written into 5e. It's a damn sight more convenient to write and say than "when current hit points are less than or equal to half your maximum hit points," and it's a convenient way to communicate with players.
Blood for the Gods is, of course, all about defining a playstyle. I thought about doing Dex + Wis for AC, but realized that I really wanted these guys wielding heavier, more intimidating weapons, and those all require Strength. I don't want to go down the road of a subclass pushing clerics toward Strength, Dex, Con, and Wisdom, so I gave them heavy armor proficiency instead. It's a bit bog-standard, but my other options were all more complicated than seemed justified. In earlier editions of D&D, clerics could only use bludgeoning weapons because of strictures against drawing blood; since this domain flips that assumption, I also flipped the weapon preference.
The Blood is the Life is here in part so I can quote Renfield from Dracula, a blood cultist if there ever were one, and also to provide the cleric with extra survivability, since so many powers tell them stay bloodied. Or you can think of it as playing like Kylo Ren.
Channel Divinity: Bloodgift is kind of here to make your allies feel better about the fact that you're not wasting precious bodily fluids spell slots healing them. I see it as being especially friendly in concept to orc clerics, driving their bloodied allies into a frenzy, but also working for clerics of Ilmater, who urge their allies to fight through the pain. I know it's not customary to have Channel Divinity powers scale by level, but opportunity-attack damage doesn't scale evenly for all classes, so let's see how this does. (Technically it's not an opportunity attack, of course, and War Caster doesn't apply here. Suck it, Almost Every Caster's 4th-level Feat Choice.)
Mighty in Vengeance is the serious payoff for staying bloodied as much as possible. I wanted a way to improve all numerical effect values, and this is what I came up with: a floor on every damage or healing die you roll, without a lot of time spent rerolling dice since it is every effect die you roll.
Red Ruin is your standard 8th-level damage kicker. I thought about making it another while-someone-is-bloodied conditional, but by this point it's getting a bit redundant. As I've done in other cleric domains, you get both the Caster Cleric and the Weapons Cleric versions of this feature, because it feels better to me that you can play either way, or switch between the two.
Blood and Souls is here because I finally needed to include some thematic element of sacrifice in this subclass. The problem with not having more feature space to play with is that I don't have that many places to put things, but there's a lot of conceptual ground to cover in the theme of blood cultist. Anyway, this is the least goodly feature in the whole domain, as it pays you for delivering final blows. I wanted this one kind of cleric to have something vaguely resembling Arcane/Natural Recovery, even if this one has a requirement and restores fewer total spell slots. (I might rework this to "total spell slots up to half the CR of the creature, none of which may be higher than 5th level," or something to that effect.)
I had another Channel Divinity that I couldn't get quite right and didn't have anywhere to place:
Channel Divinity: Bloodtheft
Starting at ?? level, you can use your Channel Divinity to make blood flow all the more freely from your foes' wounds, a sacrifice to your deity.
As an action, you call your deity's name, and up to five enemies within 30 feet, with current hit points less than or equal to half their maximum hit points, lose 1d6 hit points from bleeding. They suffer this damage again at the beginning of their turns. At the end of each of its turns, an affected creature may make a Constitution saving throw against your spell saving throw DC; on a success, the bleeding effect ends. The bleeding effect also ends if the target receives any effect sufficient to stabilize a dying character.
This feature has no effect against bloodless creatures, such as most undead.
This version isn't quite there yet. I like the idea of a bleed effect, but it doesn't scale with you as you advance well at all. Probably I would be better off with a short-duration poisoned condition rather than damage.
I thought seriously about writing a new cleric cantrip just for this domain, much as I did for the Spirit and Exorcism domains. It would be called something like spasm or bloodtwist, and... I dunno, maybe it would do better damage to targets at full health, because focusing fire is usually so tactically preferable? It seems to go against the mechanical throughline of this domain, so I'd need to justify it carefully.
Ultimately I'd love to see this come to a place where clerics seriously consider making a blood sacrifice after a long rest, so that they start their adventuring day bloodied and try to stay that way all day. (This is only okay because it is a game. Self-harm is not a fun or awesome thing in real life.)