What Attribute Determines Power?

I know Endurance determines Health, but Power? Is it Intelligence?

If I’m understanding your question correctly, you’re asking what stat influences max power and power regeneration. If that’s right, then I think I can say that power is not influenced by any stat. Intelligence can help indirectly by increasing the chance of a free skill use, but power shouldn’t be too much of a problem with the right party configuration.

There are, however, items which help with power. Skulls, orbs, and other offhands have a bonus to power regeneration, and rogues can wield bandoliers which grant them +10 to maximum power. Unfortunately, items with power regen are much less common than they were in Book of Dread (probably because the stat was pretty OP in that game, but I digress), so boosts to the stat are limited for characters that aren’t mages/healers. Anyway, hope this helps.