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furies or megaras, the difference is small, I think megaras have more damage, so I prefer them, but it's not crucial.
Dwarven warriors are one of those slow units, and megaras can break through them. You'll have to run around a lot; you can take some single units to distract them, but in the end, they can be defeated.
Battle Discipline increases the number of spells cast until all your troops are killed. That is, the opponent waits three turns while they are invisible, then kills the first single units and then the next single units. All this time, boulders and lightning bolts from the sorcerer are flying at them. In this sense...
As for a strong hero, there are many options. Sinithar is my favorite with his innate lightning spell. Or Vaishan with luck and great archers. At one time, Leto was also a favorite, especially if he gets lucky with plague at the beginning of the battle. Something like that.