Both the Master and the challenger pick 3 non-Pillar/Tower cards which their opponents cannot use during the Final Battle. Banned cards are revealed 5 minutes before the battle starts.
Something like that could work I think.
if i pick - for example - deflag, immolation and rage potion, its pretty impossible to make a fire deck without at least one of these cards, so 5mins seem a bit less time for me, maybe 3 days is better.
and i also think, the battle of the challengers also needs a restriction in a way, maybe there the master ban 3 cards for all the challengers, so noone has an advantage.
i still think that system is far far away from the reason, i want another format than all cards allowed, my intention was making the deckbuilding skill much more important, not the skill of choosing the right cards to ban. maybe every challenger and the master bring in ideas, and then there is a voting (only the challengers and the master), which 3 cards to ban.