Future expansions.

No way, what are you talking about! No need for double casting – that’s just terrible. I already crush everyone with my mage, and if you let me cast spells twice, it’ll turn into a massacre! I could understand it if the ability to use a second spell appeared when the mana bar was refilled during battle, and the bar itself refilled slowly and only when magic was used (and the level of the mana bar would affect the level of spells that could be cast and/or the mana cost/bonus).