Finished the game at impossible with a warrior today (1st attempt, started at impossible, because I know KB: Legend 100%), basically the no losses is easy as hell once you get a proper army + a decent amount of mana.
My main strategy was:
1 tank - royal griffin (best tank for a warrior In my opinion, can summon Angelic Guards - very nice unit - can Cheer = the best buff in the game)
Damagers:
Hunters - avaible once some castless were conquered
Elves - a bit weaker version of hunters, still very powerfull
Skeleton Archer - HUGE damagers, with items +talents they got almost 70% crit !!!! did not use dragon arrows, cause it was nerfed badly in AP, in late game with a crit (70% of the time) they did around 25,000 dmg each round if the enemy was in range.
Inquisitors - I know they suck, but the only archer worth swaping for a warrior was a goblin.. and elves hate undead and orcs so the loss of morale was too great, and the skeleton archers were my primal dps)
The most important thing : Turn Back Time spell (30 mana for a creature lvl 4), once you have it you can take lethal or invincible monsters without any worries, with no losses.
Basic strategy:
1) You send griffins without attacking close to the enemy ranged units to block them, and cast summon Angelic Guards if the enemy is very strong, or cheer if you know the battle wont last long.
2) You rape the enemy with your archers, starting with their ranged units
3) at turn 2, put your inquisitors on wait, attack with all the rest, then when the enemy will move its every unit cast Turn Back Time on Royal griffins.
4) Turn 3: if you are low on mana, use your dragon to replenish it or cast Calm Rage.
5) Repeat steps 1-4 if necessary.
The only casualties you will have is when facing enemy heroes who cast offensive spells.
The reason why I used Royal Griffins instead of paladins:
- they counterattack every time, combine it with the +counterattack talent which gives +20% crit I think = pure awsomeness
- they fly - no need to worry about obsticles
- better speed and initiative then paladins
- cheer = best buff in game, not to mention the bonus to all humans (only inquisitors in my case..)
- can summon Angelic Guards, great units for blocking
The companion I used was the guy who gives bonus to archers crit chance, he gives 25% at the end = that is a great boost
Was also considering to make dark knights a tanking unit, with the artifact which makes them counterattack each time, but the flight+cheer+summon of a griffin owns.
IMPORTANT: this unit setup was made with the +1 morale bonus from the paladin tree talent, crown of elves (supressed every time the morale of the crown went to 0) = with those two, elves suffer no penatly for having an undead in the party, later on I got another great item +1 morale of all archers +dmg or sth. When choosing items look for +phisical dmg or dmg of all archers etc, or a +1 fire dmg item (from the demons set)
With the money you save that way, you can really abuse the rune shop, I had like 4,000,000 gold at one point (used treasure hunt in each battle 3 times) and bought runes for it and almost maxed out all three talent trees (finished the game at lvl 55)
Hope it helps, now starting a mage at impossible :>