Sounds different, but fun. I would play it
Only thing is, I would make any battlefield sumons you might include really hard to cast, because they would be pretty good in that kind of situation.
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I just realized that anything flying would be absolutely awesome with this mod. And almost anything with ranged attack. Just think: enemy attacks, your mages summon 2 Air Elementals, enemy army routs. Because they had no time to summon anything, the first death routs them all!
Yup it would be interresting, because instead of dom2 based on (mostly) army, here it will be character base game. So you can scare off an opponent by slain one of his summoned creature. It's like showing 'Do your worst, I can handle it no matter what' attitude.