I get a lot of my gems from the monthly multiplayer (only if you already have the skins) and the beat the bosses 3-5 times. Coins you can get from just either logging on everyday for the monthly coin reward (log in 20 times) for 500 coins or grinding story mode 89 (I think) which is brimstone. You could just do all the tasks to get gems and use them to open legendary chests for 20-30 megamorph gems (the dark gems), lots of coins, 50% of your gems back (sometimes) and also a chance of an elemental. Hope this helps 😊
