You can spend your gems on useful items in the shop. Buy chest to get rare cards for your research, time skip potions (please note they can’t be stored and will take effect immediately after bought), and elixirs.

Keep in mind that cards and elixirs bought in the event store would disappear after the end of the event and will not be transformed into regular mine resources.

If you would like to receive additional bonuses like spins or huge mystical barrel deliveries without watching the ads, you can buy the “Remove all ads” offer at the top of the store. It removes all the ads from the game (all the ad bonuses are still obtainable, you just don’t have to watch any ads anymore), gives you 500 gems, and a legendary chest!