Hit Dice and Magic

I have written before about finding more uses for Hit Dice in 5th edition D&D. Here are a couple more ideas.

These make more sense if you consider a HD to be some manifestation of your will. Normally you use it to pull your own body back together from injury, but why not spread it around?

Wizards Copying Spells

Instead of spending 50 gold per spell level on rare inks and such to copy a spell into a wizard's spellbook, spend 2 HD per spell level.

You can split the effort across multiple rests. (1st-level wizards must do this.)

Specialists only need to spend 1 HD per spell level for spells in their school.

This seems like a reasonable extension of the wizard's will. I also tend to play in resource-scarce settings where there's never an opportunity to buy or make these inks. Also makes wizards a bit squishier, or opens up interesting possibilities around periods of vulnerabilities for wizards.

Instead of Costly Components

I've never really been a fan of the component system for magic since 3rd edition. That's probably a different post.

Require the caster to expend HD instead of requiring material components with a gp cost for spells. Most spells which require costly components are creating some kind of lingering effect or awareness or imposition of will - if you think of spending HD as imbuing something else with a sliver of yourself this works out fine.

Quick look at the spells with costly components in the SRD, I would break them down like this:

• 1 HD: Arcane Lock, Augury, Divination, Find Familiar, Guards And Wards, Illusory Script, Magic Mouth, Magnificent Mansion, Nondetection, Programmed Illusion, Project Image, Teleportation Circle, True Seeing
• 2 HD: Arcane Sword, Circle Of Death, Clairvoyance, Continual Flame, Find The Path, Glyph Of Warding, Greater Restoration, Identify, Legend Lore, Magic Circle ,Magic Jar, Raise Dead, Revivify, Stoneskin, Warding Bond
• 3 HD: Awaken, Contingency, Forbiddance, Forcecage, Hallow, Heroes' Feast, Holy Aura, Instant Summons, Planar Binding, Reincarnate, Resurrection, Scrying, Shapechange, Simulacrum, Symbol
• 4HD: Clone, Gate, Sequester

Then there are are a few weird ones:

• Astral Projection: 2 HD per subject
• Create Undead: 1 HD per corpse
• Imprisonment: 1 HD per HD
• Secret Chest: Breaks all the rules. At a wash, the creation of the miniature chest takes a HD, and the creation of the large chest takes another, which it keeps. If you lose the large chest you lose a HD. Adventure onto the ethereal plane to get it back.
• True Resurrection: 1 HD per HD 

Your wizards will look at this change like some kind of godsend, until an expedition doesn't go as planned, or an assassin sneaks into their home following the theft of a spellbook.

Low-HP 5e

Some quick ideas on how to lower the HP cap for PCs and NPCs. There's lots of discussion around why you'd want to do this, but some reasons you might consider:

• De-emphasizes combat.
• Emphasizes social solutions and creative problem solving.
• Encourages DM to come up with interesting interactions with NPCs.
• Up the realism.
• Monsters stay monstrous.
• Don't have to worry about balancing encounters.

Some relevant discussion here. I also swear I read a good article about capping HP in LoTFP or other such OSR recently but I can't find it for the life of me.

Note that while these changes should be applied to most NPCs and humanoids if they're being applied to the players, they should not be applied to monsters.

Constitution == Max HP.

Probably the most drastic change. A 1st-level character under this option is likely to be a little tougher than by default, but it's slow going from there. Only by increasing your Constitution score will your max HP increase, and even then it's a soft cap of 20 and a hard cap of 30.

I would probably limit characters to a single HD under this system.

This has the added benefit of being simple to apply to NPCs.

Ability Score Increase == HD.

Every four levels or so, you get another HD. Your max HP increases like the default rules.

This should produce gradual progress, and not require many other changes, but still have PCs with only about a fifth their default HP resources.

For NPCs you could probably just divide their HP and HD by 5 (round up).

Interesting side effect: High-level Fighters will end up with more HD than other classes.

Front-Loaded

You get HD and max HP normally until level 4 or so. Then you stop.

Pretty easy to eyeball this for NPCs. Since there's a cap you could even make a little table of Level/Con Modifier. Like this!

Con \ HD	1	2	3	4+
-2	2	5	7	10
-1	3	7	10	14
0	4	9	13	18
+1	5	11	16	22
+2	6	13	19	26
+3	7	15	22	30

You'll never have to track more than 30 points of damage on an NPC under this approach.

Small Max HP Per Level

Your max HP increases each level, but only by an amount fixed by your class, or your Constitution modifier, whichever is greater (minimum 1).

I'd probably set the per-class level based on a ranking of HD, so:

1. Sorcerer, Wizard
2. Bard, Cleric, Druid, Monk, Rogue, Warlock
3. Fighter, Paladin, Ranger
4. Barbarian

NPCs that use d8 for HD end up with about 40% of their default HP.

Magic Considerations

Under any of these, spells that grant HP increases like aid and heroes' feast become much more powerful. I would consider reducing any increases to max HP based on the spell level, or they'll likely become something the party feels like they always have to cast, and that's not interesting. Aid might grant 2 HP per level of casting instead of 5, for example.

Low-level healing spells remain useful for much longer, which means more high-level spell slots are available for other types of magic.

High-level destructive spells become one of the few hopes of defeating high-level monsters in direct combat, which feels right in a certain kind of game. Wizards and sorcerers become more like the glass cannons of older editions.

Other uses for 5e Hit Dice

Hit Dice in 5e seem underutilized as a resource. I have no idea if this is intentional design, but here are some other possibilities.

• To power class abilities.
• Berserker barbarians' Frenzy ability could burn HD instead of causing exhaustion.
• A paladin's lay on hands ability could let them spend HD on another's behalf. That seems a little more sacrificial to me, and is swingier that picking an exact number of HP.
• Probably some sorcerer abilities, but who cares.
• Maybe a warlock invocation that lets you burn HD into spell slots. Seems like an appropriate risky sacrifice for power for that class.
• Magic item fuel. I did this once already.
• You could make attunement to an item in general require investing a HD in it, if you wanted to reduce magic item use a bit.
• Healing potions that let you spend hit dice would scale automatically to the character using them, based on HD size and Con modifier.
• Ring of X-Ray vision could eat HD instead of inflicting exhaustion.
• Instead of reducing max HP, damage caused by certain undead could also use up a hit die. They come back on their own at a long rest already, so no special rules needed on the monster. If the undead can create spawn, they do so by killing a creature with no HD remaining.
• Potions that restore HD.
• Diseases could eat away at HD.
• Spells that allow HD to be used, like 4e healing surges. Healing Word seems like an interesting candidate.