Blood Mage, 2nd Variant (5e Feat)
From D&D Wiki
Prerequisites: Constitution 13 or higher, able to cast at least one spell and/or have ki points or similar
Every being, living or otherwise, has some kind of power animating it, and you have learned to harness this power.
From now on, when you perform magic, you can choose to expend hit points or hit dice in place of the normal cost of the spell or ability. If you use hit points, you take damage according to the table below, and your hit point maximum is reduced by the same amount. If you use hit dice, your hit dice maximum is reduced. None of the damage caused by Blood Magic can be reduced in any way except with this feat's effects.
|Spell Slot Level||HP Cost||Hit Die Cost|
Alternatively, as part of a long rest, you may gain temporary spell slots by spending hit points or hit dice equal to half the cost of the related level (rounded up). Hit dice spent this way can not be used to heal during that same rest. The number of temporary spell slots you're able to gain in this way is equal to your proficiency bonus.
You cannot use Blood Magic to cast a spell or use an ability at a higher level than you have spell slots for unless you have temporary spell slots of at least the appropriate level that were granted by this feat.
For instance, an Earth Genasi can cast Pass Without Trace as part of their racial ability. Since it is a 2nd level spell they need to currently have a Blood Magic temporary spell slot of at least 2nd level in order to cast it using hit points or hit dice.
Similarly, a 7th level Wizard can use hit points or hit dice to cast Fireball at 3rd or 4th level, but not at 5th level unless they have a Blood Magic temporary spell slot of 5th level.
If you have ki points, sorcery points, or a similar mechanic, you may use Blood Magic to activate their related abilities. To do so, you must take damage equal to twice the cost and your hit point maximum is reduced in the same way.
Immediately after dealing piercing, slashing, or necrotic damage to a target within 10 feet of you, you may use a bonus action to absorb a portion of the victim's life force. Doing so decreases the hit point cost of Blood Magic by half the damage you dealt (rounded down), down to a minimum of 1 hit point. This decrease lasts until you finish a short or long rest, cast a spell using Blood Magic, gain a Blood Magic temporary spell slot, or until the next time you deal piercing, slashing, or necrotic damage, after which the cost decrease is lost if you do not use this ability again. If you do, then the new cost decrease replaces your current one even if it is lower.
A creature that is magically linked to you such as a familiar, conjured creature, undead minion, controlled/possesed creature, or a golem of your creation, can activate this effect with their bonus action if they dealt one of the above damage types to a target within 10 feet of them and give you the resulting cost decrease as long as you are within 10 feet of the linked creature. You do not lose your current cost decrease if the creature chooses not to activate this ability.
After activating this effect, if you or the creature that dealt the damage are within 5 feet of the target, they take additional necrotic damage equal to your proficiency bonus. This damage ignores resistance and immunity.
When you finish a long rest, your hit dice maximum returns to normal but the hit dice are not regained in that same rest.
Additionally, the decrease to your hit point maximum caused by Blood Magic is removed but the hit points lost can not be healed in that same rest.
If you are playing a class or subclass revolving around blood magic or manipulating life energy, then when you use this feat you can choose to reduce your current hit points or hit dice OR their maximum. Reducing your maximum does not reduce your current hit points or hit dice unless doing so would lower your maximum below your current amount. If a class feature allows you to lower the hit points or hit dice of a creature other than yourself, you can choose to reduce their maximum instead, reducing their current amount as well if it would be higher than their maximum. Also, due to how strenuous it is to use Blood Magic to this degree, hit points and hit dice you spend or take from other creatures with the features of that class or subclass cannot be regained following the previously outlined restrictions except through any methods detailed in that class or subclass.