Reduce passive mana regen to require 24 hours for 100% mana regen. Fully resting doubles passive regen (12 hours for 100%). Regular resting increases regen by 50% (16 hours for 100%). Increase mana pool or decrease spell cost so an apprentice level mage can complete a 'basic' dungeon (12 average mobs). Scale mana pool growth with level, so more experienced casters can handle more. Why I'd like to see this - Today, mana refills from fight to fight, so as long as you can make it through one fight, you're prepared for the next. I prefer a magic system where excessive magic use has a real cost, and a risk. Sure you can squash that spider with the biggest spell in your arsenal, but why not just hit it with a stick so you can survive the dragon that's planning to jump you once you make it out of the dungeon?