Hit Points For Spell Use

OK, here's my initial plan for hit-point costs for spell-use.

To cast any spell, it costs you (1d6 + spell level) points, which comes off your maximum hit-point total.

Note that point: off your MAXIMUM hit point total. That means that magic use may actually cost you hit-points, but more importantly, it will affect the amount to which you can be cured.

Example: you have 50 hit-points, and you cast three level 3 spells which ends up costing you a total of 20 points. That means that you now effectively have only 30 hit-points. Just like physical damage and fatigue. The difference is that if you then take another 10 points in a fight, and get some magical healing or use one or more of your healing dice, you can't heal up past 30 points — your new Hit-Point Maximum. If you use more magic, your Hit-Point Maximum will drop still further.

Note that if you've taken 10 points of normal damage (to 40hp) and then cast a spell that drops your Hit-Point Maximum to 45hp, you won't immediately lose any more hit-points. It just means that you can't be healed up to your usual 50hp.

If you then cast another spell that drops your Hit-Point Maximum to 39, you'd actually lose that hit-point, because your new Hit-Point Maximum is lower than your current hit-point total.

A spell that requires Concentration to maintain will have to be paid for again if circumstances require a Concentration check (though it doesn't require new verbal, somatic or material components to be expended). If the check fails, you won't lose any hit-points, but of course the spell effect stops.

A Long Rest will return your Hit-Point Maximum back to normal, but nothing else will (unless I make up a spell or magic item or something that will do it).

It's not all bad news though. I'm doing away with spell slots — I think the hit-point cost is limitation enough.

I'll also be designing some magic items that can be used as hit-point sinks (i.e. that can be used to power spells before you have to use up your own precious life force) — probably along the lines of ioun stones and the like — some of which can be recharged, others of which will be disposable items.

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Modification

I was thinking about what Andrew said about there being no point in ever using a lower-level casting power, apart from the miniscule difference in hp cost, and I think this might answer that:

We return to daily spell-slots as written in the rules, but they are no longer an absolute limitation; they're rather pricing bands or multiples. The casting cost increases if you exceed the number of "safe" slots available, as follows.

Let's say, for example, you have one 4th level slot, two 3rd, three 2nd and 4 1st-level slots.

• You use up your 4th-level slot, at its standard cost of 1d6+4. If you want to cast a second 4th-level spell, the casting cost rises to 2d6+8. If you want to cast yet another, it rises to 3d6+12, and so on.
• You have four 1st-level slots available, so the first four level one spells would each cost 1d6+1 to cast. The next four would cost 2d6+2, and the next four would cost 3d6+3.

Is that clear? It does mean that you'd have to go back to keeping track of how many spells you've cast at a given level, but life is a vale of woe, and man is born to suffering as the sparks fly upward.