Save your gems, truly save them. After the first 5k gems that it you're drip fed gems at a minuscule amount. Paying for more gems then is really the only way to get more so you seriously need to think about which deck you're going to build and play before opening random packs. I previously rated 3 stars now rating 2 stars because of the sheer slowness of the duel. Literally sitting and waiting for a solid 5 minutes for the other player to act or complete a series of actions