Chainmail Style Casting

From publisher blurb: This issue? The original wargame Chainmail had casters whose magic was about as reliable as a catapult shot. This takes that 'roll-to cast' mechanic and turns it into a more reliable system that allows casters to have access to more magic while giving them options as to how they use it. Their power drains over time, and drains much faster when they cast more powerful magic.