Can't play for long without spending. Takes too long to get energy (25 minutes for enough energy for one round, which can be as short as 1 minute of play) and there are multiple rounds per level. Same with multi-player coin-paid rounds. You can get 200 coins every 6 hours with an ad. Costs 80 coins per lowest level multiplayer game, so you can play 2x. If you come in last just one time, you won't win enough gold for a 3rd game.