Well, the most wickedly entertaining playthrough I have ever had with the Mage in KBAP has come to an end.
It took a while, since I was lingering a lot. But in the end, all went as I thought it would. It is all about knowing the game, knowing the game mechanics and knowing what works best and when does it work best.
The Mage gets a really tough time throughout the game and starts to shine around lvl 40 when you can upgrade most of the equipment and get spells like geyser and death star. To remedy that, the best you can do is to make a playthrough where there's a Verona map on Scarlet wind and start kiting the map guards till you open up the entire map. This usually means at least 5 hours of uninterrupted loading, saving, swearing, anger, and so on. But in the end it's worth it, as it provides a very strong and stable playing environment from level 10 to 40.
So I did the same. I did all the quests that do not require fighting (except the ones on elon and nameless) and started the fighting on lvl 18 with a bunch of items already purchased as well as a very strong lineup - Tirexes, Archmagi, Paladins, Inquisitors and Gorguanas, backed up by Knights and Demonologists. With this setup it's impossible to suffer casualties up until lvl 30 or so. After than, some enemies start posing a little trouble. However, having opened up all maps, I had target, stone skin, fire rain and that was more than enough to get me through the harder battles. Starting powerful also gives you the opportunity to use higher damage traps right from the start. In the beginning, there were battles where I raised the trap counter by 3-5 points in one go, as it was a snap.
The game was a breeze, actually. The only tough spots are as usual, the castles and the bosses. Another tough "spot" was Elenhel. On Impossible, he's simply wickedly overpowered and you have to confront him on lvl 40. 115 necros, 187 Archmagi, 250+ Demonologists, 328 Druids... They hurt a lot, and his geyser was dropping my stacks by 1/4 per cast. In the end, the Paladins prevailed. The tactic was simple - target + stone skin on the paladins so that they suffer as less damage as possible from attacks and geysers and then making sure that no other unit dies. Even if in the end you end up with just a few units, this means you did it good, and the resurrecting can begin. I also kept mu back line units very close and used paladin phantoms to do quick resurrections when I saw things were going bad.
Before I start on the bosses, you should know that there is one extremely useful item in the battles with them. That is the rage eater, so if you see it, buy it! Since you can't summon the dragon, you can't transform rage to mana. Well, this little toy will do that for you. It's 5 for 5, but it's better than nothing.
I also made sure I have a +20% leadership scroll for the last 3 boss battles, as well as any other stat-boosting scroll available. Since I was digging all the time, I had plenty.
For the bosses... Spider is a snap. Demonologists spawn demons, Knight with stone skin + magic shield near his left legs, Paladins with stone skin near his right ones. Paladins hack the Giant spider all the time, Knights help from time to time against the growing spider stacks.
Driller was a pain in the first go. But then I got inspired and made this party - Paladins, Knights, Archmagi, Inquisitors. 4 units, the width of the bridge. If there are 2 units in a row, that's simply begging for a gun shot that usually results in a lot of damage. So, like the spider - Knights with stone skin and magic shield near his driller hand, Paladins near his other hand. When he summons droids, I used the archmagi and inquisitors to beat them up. When he summoned Repair Droids, I left them be, simply reduced them to smaller stacks so that they don't pose that much trouble. Then, when the driller was down, I could ress at will.
The tactic against the Dersu-Kumatu Frog is the same. If you have the Healer's Jacket (pretty common item), put it on without thinking! That will reduce the damage your units take from the frog's spits. After that it was the same. I left a royal snakes stack alive after I killed the frog and went on resurrecting. Since royal snakes have no retaliation, you have a lot of time to do that.
Zilgadis was easy. Equip items that provide magic resistance and/or stock up on troops with decent magic resistance. That will deal with his mass attack, since it inflicts magic damage. I used the mirror shield + anti magic diploma and that was more than sufficient. Then it was simple - Knights with Stone skin near his left arm, Paladins with stone skin near his right one, the other 3 units (Archmagi, Guardsmen, Horsemen) hack at the towers and/or anything they spawn. I finally left one evil gremlin (he simply didn't spawn a friendly one later on) tower and ressed everything.
K'Tahu was another deal. All his attacks are physically based, so you need high physical resistance. I did it with this lineup: Knights, Paladins, Horsemen, Guardsmen, Demonologists. It was really tough, but with the rage eater, phantoms and protecting the demonologists and guardsmen from suffering major losses (stone skin help a lot here) I did it. I also had Knights on his weak spot and Paladins (higher def) on his protected side. Paladins had Stone skin on them all the time so that they take as few damage as possible. Regretfully, I had to swap the companion for this battle - BB Elenhel, hello Agvares. You NEED both the Singing dagger and the Inquisitor's Sword equipped, so that you have more paladins available. You will suffer casualties, but when K'tahu is low on HP, wait will he summons a stack with Gorguanas with it, then kill him. Finish off the summons, and leave a few gorguanas alive, then start resurrecting. The rage eater will provide sufficient mana for the task (NOTE: works until rage falls below 10, not 5! Also when the rage and mana income becomes 0, it stops working. So plan accordingly).
Baal was another matter. If he starts summoning stack after stack, you'd better restart, because after summoning a stack he won't be able to hit you directly, so he'll throw his sword, which is HIGHLY undesirable.
What you can do, is to be aware of his capabilities and his behavior. If there are 2 stacks one behind another on his line swinging there is a big chance that he will do just that. So I used stone skin only on the Knights, Paldins and Horsemen, while the Archmagi and Demonologists provided cover with magic shield and summoning. Then I put the Knights and Paladins right in front of him and put the Horsemen behind the Paladins or Knights, whatever was available. Believe me, losing 5-10 horsemen in such attack is highly preferable to having Baal summon a ton of Archdemons, Executioners, Demons, and so on - besides, you can always buff them up with magic shield and lose only 3-4 of them. I also made sure that the Knights and Horsemen in Bill Gilbert's army had Stone skin on them as much rounds as possible. When I exhausted my dual casts, I left his horsemen to die and concentrated on doing this: 3x stone skin for my paladins, knights and horsemen and 2x 15-mana phantoms so that there is always a unit behind unit to tempt Baal to hit them both rather than throwing his sword or summoning enemies. Well, both of the latter actions cannot be avoided from time to time, but that provides valuable rounds to hack at him with more than 1-2 units. I also made sure that when Bill Gilberts' units died and Baal was low on HP, to leave an Imp stack alive so that there is something on the battlefield (especially one with no-retaliation!) before I start resurrecting. In the end, that tactic worked perfectly.
And there it is. Mage, Impossible, lvl 57, no losses whatsoever
I've added screens of the build and the result, as well as the save game just before finishing the game to show that everything is fair and square