@john_crapper You didnt mentioned what else spells you have at disposal. Death star is great if you have 1 lvl of tactics to arrange your units in first turn, after that piranha shoal is also great spell for it`s mana cost, fire rain as you already siad. But all this doesnt mean much with your 14 intellect (or was this number wrong?). For mage trying to go on impossible with just troops i`m not sure is that what you trying to achieve, or just didnt find enough +int items. Mage is best high int spells dmg, or support build for high resistances and other beneficial spells in my opinion. If you want to go mage army build, i think you`r in for a fun time
Because she simply doesnt have enough lds or att/crit% to do some serious dmg with just units.