Just finished impossible as mage. From begining i used fear, fireball, royal snakes and other snakes with frog wife and at lvl 9 arrived on freedom islands and clear all there.
I was really unlucky with ice snake or fire rain so i decided to rush for elven islands. I did not kill anything in Kordar. So at lvl 14 terrible battle vs castle in taron mines.
Finaly elven lands so i found ice snake scroll somewhere in the middle while sneaking even lands of death. I found fire rain in guarded castle thx dryads and sprites mostly. All enemies were overpower or impossible after then fight match or strong party was pretty easy. At 22 lvl battle vs karador castle was really hard. Then i went to clear Kordar, mines and Demonis and everything else
Good spells: fear, slow, sheep, blind, magic spring, phantom, stone skin, doom, magic shackles, ice snake, fire rain and flaming arrow.
Good units: royal snakes, marauders, priests vs undeads, shamans, unicorns, sprites, dryads, elven archers, green red black dragons and all demons. Most time 3 dragons and archers or unicorns.
Wife feanora all the time with one 10 mana child just triyed one for my luck and still better then scrolls
Tactic:
Toughest main quest battles defending in corner and nuking by spells.
Other challanges i prefered cc meele such as sheep and doom then focused by 3 dragons slowing rest and nuking if possible.
Phantomed dryads can makes 12 turns all 1-3 lvl crazy stacks sleeping. Also easy way using higher lvls units and fear all lower still good at the end vs 1800 goblins in one stack etc.
Nice challange at all. Id like to see yours records and story