"only XL-3"

Request to the organizers: please provide the following information:
Who starts the bidding, what colors are available, and when is the best-of-three match played?

3. Random castle selection + bidding
The host generates a pair of random castles using a special button. Immediately after generation, each player can request a regeneration once for 500 coins, which will be deducted from the opponent. If, during regeneration, at least one castle is repeated, the same player can (but is not obligated to) request a free regeneration until a new pair of castles is generated.

Regarding the additional information added to point 3, we encountered the following situation... first, the opponent paid 500, then I did, and then a pair was generated, and one of the castles was the one the opponent had initially banned. Does he still have the right to regenerate, or not?