In my opinion, one of the most important skills, especially for mages, is Defense. The skill is good in itself, and it also fits very well with the mage's playstyle (defense, as it provides 3 ranged attacks, and with Fire Warriors, even 4). Moreover, Expert Defense reduces damage by 30%, which, if I'm not mistaken, means that the lower the Defense stat of the hero and troops, the MORE USEFUL the Defense skill is (because with low defense, units take more damage, and these -30% provide significant help). This is especially true for mages. Of course, the 2% chance of Defense appearing is a problem, but this problem is easily solved by choosing Razazak. Following the same logic, it probably isn't worth taking Attack (if it happens to appear), although Battle Fury and, especially, Ranged Attack look very appealing. Spell Power is a must-have skill, but I would like to ask about this: what is the point of leveling up Counterspell? After all, if you use it, that turn will be counted as a regular hero attack, meaning that the Spell Power skill doesn't work at all. Therefore, after using Counterspell, a Necromancer with Expert Spell Power will first dispel the Counterspell with a cheap ranged attack, and then manage to attack again before the mage's turn.