I'm in the process of homebrewing an arcane half-caster for one of the players in my next campaign. One point that concerns me is whether I should give a d10 or a d8 hit dice. I want it to be comparative to existing half-caster classes and subclasses but there is a bit of a mix.
My belief is that the presence of cantrips and/or 5th level spells has an impact on the HD. Essentially that the half-casters with the most magic get a d8 while the rest receive a d10.
Half-casters I am comparing to:
| Class (Subclass) | HD | Max Spell Lvl. | Cantrips |
|---|---|---|---|
| Ranger (any) | d10 | 5th | No |
| Artificer (any) | d8 | 5th | Yes |
| Paladin (any) | d10 | 5th | No |
| ^ Fighter (Eldritch Knight) | d10 | 4th | Yes |
| ^ Rogue (Arcane Trickster) | d8 | 4th | Yes |
My current plan give cantrips are 5th level spells and d8 HD based on the comparison to other classes. However I'm not sure if I have overlooked something else.
When selecting hit dice for half casters, what factors should be considered?
^ These subclasses are technically not half-casters and share the HD of the parent class. However I feel they are still a relevant comparison to the class on thematics and overall combat feel.
Best Answer
The dividing line is not spells, but weapon combat (especially melee).
In your grid you can see examples of classes that get 5th level spells and have a d10 hit die and classes that only get 4th level spells and have just a d8 hit die. You can see classes that get cantrips & d10 HD, and classes that don't get cantrips and only get a d8. For that reason, it seems likely that neither of those features determines a class' hit die.
I would contend that it is instead the opposite aspect of a class that determines its hit die: its relation to melee combat. Consider the d10 hit die classes in your list: the ranger, the paladin, the fighter. Each of these classes is expected to be able to stand on the front line trading blows with enemies. Consider the d8 hit die classes in your list: the artificer, the rogue. These can go into melee, and it's an attractive place for them to be in terms of damage output, but they don't want really want to be taking too much incoming fire.
Additionally, note that the d10 HD classes all get the Fighting Style class feature, while the d8 HD classes do not. The primary role of the d10 HD classes in combat is to slug it out with foes, and their spells merely support that role.