Old sleep to gain spells system from DnD had number of flaws that hampered the fun of playing caster type class:
-Low lvl mages were gimped compared to physical classes such as warriors/archers since they could only cast One-to-Few spells before becoming completely useless until the next sleeping area.
-High lvl mages on the other hand would gain access to extremely powerful spells which would in turn make lower tier spells good for nothing. For example one could simply go into the fight and spam finger of death/power word kill and similar spells to quickly dispatch enemy and then hit sleep button just to repeat that again with out having to ever use weaker spells.
-Also sleeping for 1 zillion days just to certain area kills immersion for me since it doesn't feel realistic.
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What I would like to see?
Mana bar with certain tweaks added to it that could be give more tactical game play rather then spam your best spells every fight:
- Lets assume you have 100 mana, your powerful AOE spell costs 75 mana therefore if you use it it would leave you with little mana to spend on other spells, forcing you to decide which way will you approach this encounter.
-Cooldowns for certain spells. If much needed spell has 10 minute cooldown and you still have a long way to go in dungeon using it on group of weak monsters might not be the best idea...who knows what lurks behind next corner.
-Mana Regeneration vs. Mana Pool: this could be interesting character building mechanic. Hero skills and gear could allow player to chose will he specialize in having a large mana pool that would allow him cast greater number of powerful spells but running out of mana in the process or having rapid mana regeneration that would allow him to continuously spam weaker spells, or seek some kind of balance between the two.
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Sleeping ZzZZzZzzzZz
What could be its use? Many things, like giving you small XP bonus (10%), refilling your mana/health/stamina or what ever other resource might be in game etc.
It should also have certain cooldown added on it so that it isnt spammed, I dont know about you but I dont see my character having sleeping sickness by being able to sleep for 8 hours and then instantly do so again by hitting the sleep button.
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Benefits:
-Spell casters could keep up with warriors in dungeon by going continuously from one combat encounter to the next one without having to take a break
-More realistic flow of time
-Better tactical combat and character development.