Base Class: Wizard
The mage strode forth, wrapped in a scarlet cloak, with blood glistening on her jagged dagger. She wove the wetted blade as if she was conducting an orchestra, and the fresh blood obediently rose up to dance around her form in a tempest of crimson fury. Her laughter was a shrill and eerie sound as she drew in the swirling strands of blood, causing them to crackle as they burned—and instantly, its converted power erupted from her palms in a rolling inferno.
When the smoke cleared, nothing was left before her but scorched earth, a scattering of ashes, and the acrid scent of iron. All was silent, except for the steady dripping of blood as it fell from her arm.
The dread secrets of Blood Arcana are as incredible as they are terrifying, allowing a wizard to access overwhelming power—if they're willing to pay the crimson price. As a practitioner of these grisly arts, you do not favor a traditional school of magic, and instead focus on the ability to augment spells through the perilous spilling of blood. One who dabbles in these taboo techniques is most commonly known as a blood mage.
The term Blood Arcana is the collective name of arcane practices used to convert life force into power, also known as the scarlet arts. Most societies fear blood mages and forbid their lurid studies, considering them both wicked and exceptionally dangerous, although a blood mage is not inherently evil. The mysteries of its power are typically learned away from prying eyes, whether gleaned from the lessons of a dubious master, from an ancient spellbook, or your own grim experiments.
Many people confuse Blood Arcana with necromancy, but the truth is that the two practices are opposites. Necromancers harness the power of death, whereas blood mages harness the power of life. A blood mage is similar to a cleric focused on healing, but employs their practices in reverse—whereas the cleric uses their magic to restore life, a blood mage does the unthinkable, and instead consumes life to empower their magic.
Crimson Exchange
At 2nd level, you have learned to boost your spells with the power of blood.
When you cast a wizard spell with a spell slot, you can choose to take damage equal to double the level of spell slot you're using to cast the spell, and empower the spell with one of the three following effects (your choice):
- If the spell has a more powerful effect when you cast it at a higher level, you instead cast the spell as if you had used a spell slot of one level higher (to a maximum of 9th level).
- If the spell deals damage, it ignores damage resistances.
- If the spell slot used is 4th level or higher, you restore a 1st level spell slot.
The damage you take as part of this feature ignores resistance and immunity, and does not require you to make a Constitution saving throw to maintain your concentration. You can use this feature a number of times equal to your Intelligence modifier (a minimum of once). You regain any expended uses when you finish a long rest.
Thicker Than Water
Starting at 2nd level, you have become accustomed to recovering from damage. You regain an additional 1d4 hit points for every hit die you spend after finishing a short rest.
Additionally, you can use a dagger as a spellcasting focus for your wizard spells.
Sanguine Kiss
Starting at 6th level, you have learned to use the blood of others to bolster your spells.
As a bonus action, you can make a melee weapon attack with a dagger against a creature. On a hit, the target suffers the attack’s normal effects + half your wizard level. If the creature was not an undead or construct, you can subtract the damage dealt from the damage you take as part of Crimson Exchange, if you use it by the end of the turn. You may use this feature once, and regain the ability to use it after finishing a short rest.
Ruby Withering
Beginning at 10th level, when you affect one or more creatures with a spell empowered by your Crimson Exchange feature, you may choose to prevent all affected creatures from regaining hit points until the end of their next turn.
Scarlet Tides
At 14th level, you learn to unleash overwhelming spell attacks through the reckless sacrifice of your own health.
When you use Crimson Exchange, you can choose to take additional damage equal to the level of the spell slot you're using and become unable to regain hit points until the end of your next turn. If you do so, you may choose two of the available Crimson Exchange options instead of one, and you have advantage on any attack rolls made as part of the spell.
All other rules of Crimson Exchange still apply.

Thanks for walking through the "designer notes" on your reasoning with the feature designs here. I think we may have some small disagreements, but nothing earthshaking. I do want to clarify a few points though as I may have been a bit short on explaining my reasoning for the evaluations I gave.
Hi! Great class. This comment has nothing to do with balance, but rather some weird error on the character sheet. When taken, Ruby Withering shows up as "fsf" in the Limited Use category.
Hi Vaegrim, thanks for the feedback.
I'm honestly not sure how Overchannel can be compared to bypassing a resistance. Perhaps you're thinking of another feature? Overchannel means you deal maximum damage on the dice, but doesn't affect how your spell interacts with resistances to my knowledge. The only damage that it has that it says bypasses resistances is done to yourself. I'm not heavily attached to the resistance bypassing option here, but the alternative to bypassing a resistance is to just cast a spell of a different damage type, which you'll more than likely have available by the levels you start encountering a lot of damage resistance. The real benefit of choosing to ignore resistance is using your optimal spell against a creature, as opposed to an alternative. You also have to know that the creature has resistance to your spell in the first place. It's great if you don't have any way around its resistance with your spells, but it's not more powerful than just having those spells in the first place. And this is only 3-5 spells a day, if you're going to blow every use on doing this.
I feel it's also worth pointing out that dealing damage to yourself as part of Crimson Exchange is a pretty significant 'leash'. At level 2 when taking this subclass, I doubt many wizards will be able to have more than 14 hit points and 16 Intelligence when going by point buy/standard array. This means 3 uses of Crimson Exchange, each dealing 2 damage each. While fairly insignificant at this level, you are also very vulnerable at this level, making hit points more valuable. Furthermore, if you use all 3 uses in the one fight, you're left at 8 hit points which is not safe by any stretch of the imagination. Jump up to level 3, and the wizard now has around 20 hp, but now Crimson Exchange deals 4 points of damage if used on a second level spellslot. Three uses (both 2nd level slots and a 1st level), and you're at half your health - from only your own spells. This largely continues as you gain levels - at level 5, you will have roughly 32 hit points, but have to pay 6 hit points to use Crimson Exchange on a 3rd level spell.
I'm willing to tweak how much damage it does, or limit it to fewer uses, or only on certain spell levels, but I fail to see how the damage is a 'ribbon' by any maths. Sure, perhaps you're a dwarf, or perhaps you've taken the Tough feat, but if you're going to go with hit point boosts as opposed to something that actually boosts your spellcasting, I feel that's a fair trade and likely not the 'optimal' choice in the first place.
Sanguine Kiss does need to be slightly rephrased, good catch.
Ruby Withering is something I will think about. Given that it can affect all creatures from an area spell, it feels fairly potent to me, although it is niche in that it depends on what you're fighting. I am keeping in mind that this halts regenerative effects (trolls, vampires, etc), healing potions, and healing spells. It effectively adds the extra part of chill touch to whatever you're casting via Crimson Exchange.
As for Scarlet Tides, I agree that it needs a tweak of some kind. Having advantage on the attacks is something I feel makes it worthwhile, as opposed to taking two options from Crimson Exchange, but again fail to see how you have established that the damage isn't a limit. This does 3x the spell's level, but would you even bother using it if it did 4x the spell's level? That's 16 damage for a 4th level spell spell, and 28 damage on a 7th level. You can use it on a lower level spell, sure, but that's less impactful given that you're limited to a maximum of 5 uses of Crimson Exchange per day. If you've already taken a couple of hits, this kind of damage can be extremely risky, if not suicidal. I'm happy to tune the damage, but again I don't see how it can be ignored even at its current numbers. Perhaps if you're gaming with an unpressed life cleric, or multiple healing characters, and even then a turn spent healing you is a turn they could have spent actually doing something meaningful. I'm open to making changes, but I'd need to see some practical examples.
At the end of the day, Crimson Exchange is the defining feature of this subclass, and I don't personally have an issue with all of the subclass's features (except one) affecting Crimson Exchange. Every feature of the Circle of Moon druid (except one) affects Wildshape. Every feature of College of Swords bard affects its melee attacks. Those also happen to be among the most popular druid/bard subclasses. This focus on Crimson Exchange is one of the reasons it has to have some power behind it, because that's the core of the entire subclass, and your only real benefits come from it.
I'll be honest, I opened this expecting to hate it. Blood Magic is a really common trend in homebrew and it's usually done badly. Ultimately they're premised on the idea of sacrificing lives or health for magical power, and that just isn't balanced in 5th Edition. I think you sidestepped a lot of the most common pitfalls though, and I'm willing to at least tentatively accept something like this in my home games. I've still got a few complaints, but not enough to hold it back.
Crimson Exchange is remarkably flexible: Upcast a spell OR bypass resistance OR recover a spell slot. Bypassing resistance is the equivalent of the Evoker's Overchannel whenever you can apply it, and it works on spells higher than 5th level. The damage is also much lower than Overchannel, and I also notice Overchannel damage triggers concentration checks. Since The real limit is Int Mod per long rest, this isn't really a problem as long as you keep in mind that damage isn't the leash on this feature. The upcast option worried me at first, but then I realized you aren't allowed to boost the spell to any arbitrary spell level, just +1. That's still really potent, but not overwhelmingly so. My biggest concern with this aspect is getting access to effects through upcasting as many as two character levels early. This matters on spells like planar binding. I'd be more comfortable if the upper limit was the highest level spell slot you can cast.
The wording on Sanguine Kiss needs a tune-up. Presumably the weapon attack deals additional damage equal to half your wizard level, though this isn't stated. Since I already discounted the damage of Crimson Exchange as more of a "ribbon cost" than an actual throttle, I'm not especially concerned by the refresh frequency of this effect. Ultimately it's a wizard making a bonus action weapon attack with a dagger, that's not particularly exciting.
Ruby Withering is really niche, not many creatures can regain hit points mid fight. Additionally, this makes two of your three features that aren't Crimson Exchange which depend on it to work. I'd suggest you scrap this feature and fold the "no hp recovery" effect into Sanguine Kiss. There's a lot of room for a new feature here: a reaction when the wizard takes damage, advantage on death saving throws, or even something else that's activated by a spell you cast dealing damage. I'd suggest nonmagical slashing/piercing resistance but I think that's just a bit too potent for a 10th level feature.
Where Crimson Exchange walks a very careful line, Scarlet Tides seems to mostly step over it. As I established above, damage isn't the real limit on this feature. Even the healing limitation is only a real risk under a narrow set of circumstances. Doubling up the benefits of Crimson Exchange (every feature other than Thicker than Water either IS or messes WITH Crimson Exchange by the way), is strong enough without throwing attack advantage on as well.
Thanks!
Just out of curiosity, how did you get the beginning to stand out like that (don't know how else to describe it)?
I think keeping Sanguine Kiss once per short rest is perfectly fine. I honestly have no clue about Crimson Exchange, though.
Hey LordShadowthorn, thanks! Apparently blood-based classes are pretty popular!
In my original drafts, Crimson Exchange was limitless, but I've also limited it further than it is now too. I've tweaked it a lot, and it's very hard to balance given the wild variations between characters' hit points. In the end, I settled on 3-5 being a fair amount, but I'm certainly open to feedback. It will probably need a fair bit of playtesting.
Likewise, I'm very tempted to change Sanguine Kiss to be 'per long rest' as opposed to short rest, which also changed several times between personal iterations. All feedback is very much welcome!
To anyone who wants to try it, I will say that a wizard who follows this archetype will definitely want to invest in at least 12-14 Constitution (not that most don't do that already, given the need to make concentration saves) - those extra hit points are extremely valuable here.
This is the best blood mage class I've seen on D&D Beyond! I might have to try making one myself soon :). Only thing I can say is maybe change Crimson Exchange so that you can use it a number of times = to 1/2 your wizard level + your Intelligence modifier. That way you can use it a few more times, but not an overpowered amount (then again, that might be too many times).