I used the two races that don't have a killing buff with no trouble. Beat it first with Undead, since I didn't realize how much it had changed. (The only thing good about undead is that they are demon adjacent.) Beat it once with the Human Alliance. Their special ability turns a charge into a steamroller since it buffs the troops and you got hundreds on the field with greater power, speed, and survivability. You might have to get the right upgrades, but combining a charge with their special ability allowed a spearman charge to overrun an enemy swordsman charge.
Edit: If I remember correctly, Human Alliance bonus is +1 defence, so that helps too.
I have a basic strategy, but I haven't tested it enough on hard. Right now I have a good 7 victories and one loss, in hard mode, with elf alliance. This strategy worked for me in every level on easy, hard it has only gained me one less, but I don't know if that is because i timed my specials poorly or did not upgrade my units enough.
First, I choose one unit not to send (usually spearmen due to their speed and large squad size). The rest of my units I continually send, but down only one row. That is a major part of the strategy, only to send units down one row and to not let up on sending them. I don't worry too much about the enemy entering my side because the row I hold is well protected and will have my units entering through the enemy's side to balance the enemy units entering on my side. (If I absolutely must send my units down another row I will switch rows. This sometimes is the case when the computer decides to start sending all or most of it's units down the row I am using.)
Next, I wait for my charge and special ability to be ready. I then send my charge with the unit type I had been saving. Then I use my special. As the human race I would use the special right before my charge was going to contact short range enemy units. For the elves, I will use my special to help clear the field and allow my charge to cross. Also, I will try to send my charge right after the computer has used it's special, but this is not always possible.
So far it has been working, but I am wondering if anyone else uses this strategy or if there is a better one.
The Quests I have achieved for this game so far have all unlocked while using FireFox, so that debunks your idea @kegaumongo. All of them unlocked without a glitch. =)
Oh seriously, game does saves yet after I finished one campaign it simply reset my progress and I still have to win two campaigns to get Marcolytes instead of just finishing second. Good that at least easy mode speeds things up so I may just rush that one back.
No, as I said, game does saves correctly for me, it was just one-time bug that me made me kinda unhappy. Not sure what was the reason though, it didn't happened second time and I had no other problems. Bug just flew by randomly.
Decided to come back to this game to get the last badge; waiting a couple of months made it seem kind of like a new game and not as much just grinding to get the badge. Anyway, done.