Wicc
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Ban Gundula, Dess, and Luna (and Tsielka just in case...) and the tournament would be fine. :)
But Vik doesn't consider Luna an overpowered hero in the battle of mages year after year.
The rules should be simple, clear, and consistent with the original idea. If you ban one, two, or three heroes, questions will start: "Why wasn't the fourth one banned?" or "Why was the third one banned, he's not overpowered," and so on. For example, it's not obvious to me that Grinya is worse than Tsielka; in my opinion, he's even better.