When purchasing a hero, demons appear at a rate of 1 per second. Isn't that a bit much?
She shouldn't have any demons anymore, and neither should she.
Are you checking in single-player or multiplayer mode?
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And even so, a demon's mana isn't unlimited. And you also need 60 mana.
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You could also implement something from the third game: the "Heavenly Eye" and "Earth Eye" spells, if you remember them. Although this seems difficult, but if it were done, it would be great.
