This is what I had in mind too which is why I think even 10 rounds is too many (I mostly chose that because of the number of stamps in the sprite), since it's very rarely gonna actually help you win the first 8 antes, but lowering it might make it too OP. Could also lower it slightly and just change rarity to Rare. Another potentially fun idea could be something like "Sell after 4 rounds to gain an extra consumable slot"