Endgame. I used safe-spamming, the Archon unit, rings of mastery (5), each enchanted with +Spellcraft. From memory, that should be
(5+10) increase in SC, so, whatever they set as 'high limit' wasn't enough.
And as it was late game, it didn't matter. By that time I had an army of ogres and failed wizards, mostly kitted out. I used the precursor army of them (5 ogres and 2 failed wizards) to defeat his fire analog, without losses. Ogre resistance is nice.
What I've seen when leveling icy up: no skill tree - it's empty. 
Btw., I leveled up the city in the north in the enchanted forest area to create nice units (the +1 per essence enchantments active). Are the units players can create so lackluster, or aren't the city enchantments not working?