What difficulty and class are you playing?
My tactics as a mage is to focus my units around ranged units or units that can summon more units, then have them stall and pick away at stuff while i nuke with spells.
I mostly tank with summons + some other powerfull tanking units, like cyclops etc. I also use royal snakes and assassins etc early as they are awesome and fun
I experiment alot with different units as alot of units work with this tactic.. I only lost a few units at some hero battles so far..
My experience with Warrior is more limited as I generally enjoy spellcasters more in allmost every RPG, but I hear summons/Phantom and buffs in general work well there
Note that I'm not a crazy min maxer, I just want to have fun and try different things and play the way I enjoy the most
This games combat is very deep and there are ALOT of viable tactics and playstyles that are all viable. If you prefer any particular style, write here and we'll see what we can do to help
You'd be surprised how many crazy setups and playstyles you can beat the game with
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Outdoor Oral