I have a suggestion. Either make the Generals stronger to play on the extra and trial stages, or give us better mana regeneration and max mana as the game progresses so that if they aren't participating in battle at least they can hang back and support with spells. As of now, the only way to take on trial stages is to spam meteor level 2 and zerg the opponents, then wait about a half hour to an hour.
PLEASE let our general respawn!!! A really cool trick I found is to put an elemental orb on a magic user that isn't it's element. When you do the spells looks and affect will completely change! For example give a witch a thunder orb and its a new spell.
I don't like how your troops and hero share the same mana pool. Could I suggest that the troops auto use their spells and require no mana or something like that?
i beat a lot of stages with this setup: 2 knights on the 2 closest tiles to your tower. 3 swordsmen on the 3 closest tiles out from the knights. 3 archers on the 3 closest tiles out from the swordsmen. upgrade as needed.
you'll kill me for saying this but there is a bug where there is no duration on the poison spell, it keeps poisoning until the target is dead. I personally like it this way though :D