First of all, and to be clear, since its the Hyborian age I assume that the magic system will not be focused on spamming fireballs and chain lightning but rather on advanced alchemy involving the black lotus, poisons, curses, illusions, necromancy and summonings using relics, demon blood/sacrifices on altars.
For the sorcery system I suggest that corruption is used as the main resource(mana).
The larger the mana pool the stronger spells can be thrown.
I’m thinking that the Health pool that is corrupted defines the limit of what spells can be learned and used.
The more invested a player becomes in sorcery, the more corruption is required. Level of corruption could be tired based to open up for more powerful magic.
Tier 1 Dancing Lights, Light, Mending, Disrupt Undead, Advanced Potions/poison
Tier 2 Detect Undead, Feather Fall, Obscuring Mist, Silent steps, Summon Monster I
Tier 3 Spider Climb, Mirror Image, Obscure Object, See Invisibility, Summon Monster II
Tier 4 Invisibility, Gust of Wind, Haste/Slow, Control Undead, Summon Monster III
Tier 5 Mass Invisibility, Control Weather, Astral Projection, Summon Monster IV
(Note, the above are only examples but they all fit in the Hyborian universe)
An illusion - Light requires a minimum of 5 corruption points.
Mirror Image could require 100 and Summon Moster IV 400
The maximum “corrupted energy” mana available is what limits how much “corrupted
energy” the sorcerer can spend for a spell.
For instance, illusion - Light, if 10 “corrupted energy” is used when casting the spell it would last for 10 seconds. If 60 “corrupted energy” was used, it would last for 60 seconds.
A summoning would work in the same way, duration of how long the monster remains if not killed.
Potions could be more potent, poisons could be more effective. It would define how far and for how long you can travel in Astral Projection etc.
The Stamina pool that is corrupted would represent “energy available to cast spells”, it recharges just like the Stamina bar (but maybe slower, requiring specific food/drinks).
See image for clarification (i hope :))
This obviously comes with the drawback that Sorcery/Corruption lowers not only your maximum health pool but also your available stamina.
Strong sorcery will come at the price of a weaker body, this will create balance and increase the focus on team play. A fragile, but immensely powerful sorcerer will need protection, but can turn the tide of any battle using the powerful magic under its command.