I generally don't understand why you can't upgrade creatures...whether it's sprites, vampires, or phoenixes!? Take a look at the game stats on the Bay (where all this and much more is allowed) on 8mm: no imbalance is observed. As an example, I can cite my game today against the main favorite of the tournament "New Generation", MikeSpb. The randomizer gave a Conflux-Swamp matchup. Mike paid me 1100 to play as blue Swamp, despite the fact that all upgrades are allowed for Conflux. I understand that HeroesWorld has its own path, but I hope that the experience of other sites will be taken into account.
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Originally it was planned that way - seven rounds. Actually, five or seven. And to do it - it's simple - the one with the maximum number of wins wins.