I was thinking about a weekly event possibly for the weekend of each week. This mini-event will consist in betting a resource: gold, gems and food. that resource that bets would multiply according to each wave that you resist.
the maximum amount of gems to bet would be 5, for each 5 groups of monsters (3 monsters each group) that consecutive defeats would get a multiplier, the first would be x2, x3 and x4. the maximum that I could earn in gems would be 20. in gold the maximum in gold for betting would be 5M, the rules of the multipliers would apply the same. The maximum that can be earned in gold would be 20M. in food the maximum that can be bet would be 10M. the rules of multipliers would be the same. the maximum to earn in food could be 40M. You could only bet once per weekend for each of the resources. the waves of monsters would increase the difficulty with more runes, more rank and better relics. If you lose a battle, you lose what you have accumulated from multipliers. the battles are for survival so life and stamina do not regenerate themselves. you decide when to retire to save your progress and withdraw with what you have won.