How many spell can I cast per second.Typed out in a rush, think of it like this, ROB gave you the user two numbers, a 10 (ten) and a 10,000,000,000,000 (ten trillion). Then he gave you two slots; one is for mana pool and another is for mana regen (x mana points per year) to put the two numbers in, each in one slot. So either you have a mana pool of 10 that regenerate up to 10,000,000,000,000 mana points in a year (or 317,098 mana points per second) and excess is considered a waste or a mana pool of 10,000,000,000,000 that takes a trillion years to fill up if completely emptied (or 36.5 days to get one mana point back) .
Low tier spells like fireball can cost up to five mana points while the highest twelve tier spell Karsus's Avatar that turns the user into a god (for a time frame I supposed) might take up the ten trillion at one go. Do not worry that the small ass mana pool can't even cast a low tier spell, it can.
Is it possible to cast 63,419 fireball in one second.
Since fireball can melt metal it is not as weak as we might thought. If it is too weak to be use to fight proper enemy, the fireball can still be use in normal mundane task such as electricity generation and other stuff.
Furthermore fireball that stack well enough (assuming you can cast multiple fireball at the same time that is) might be hot enough to melt enemy itself.