What spells do you use with your mage?
Stone Arrow - Low cost, lower than Spark, it hits targets at the back row, probably deals more damage than Sparks (which doesn't hit the back row)
Fireball - Situational, good for fire dotting enemies. Direct dmg not so damaging for the other 2 non-centre targets.
Frostball - Situational chain freezing 3 targets, pretty good dmg as well but expensive for mana
Icy Shards - Great for bleed debuff. Even in endgame.
Blizzard - I only use it early game. Good AE spell hitting all targets with possiblility of freezing. Too weak for endgame.
Meteor - High damage on a single target, wounds target. Good main nuking spell if manapool is high.
Meteor Swarm - Meteor on 3 targets, wounds all targets. High mana cost
Thunder Storm - Good early alternative AE spell. Hits 3 random targets. Damage roll same for all 3 targets, doesn't dissipate unlike Fireball or Frostball. Stuns enemies.
Energy Absorption - Compulsory spell for me, drains mana from certain enemies. Saved me tonnes of pots.
Inferno - Hardly used, but I use it if there are many weak targets and the fire dot can kill them easily.
Hammer of Destroyer - Max ASAP. Wounds enemies and bosses. Compulsory for easier boss fights.