Rare and Legendary Chests 2nd Chances
I don't know if anyone else has tried it yet, but just a heads up.
After you open a rare or legendary chest and the game offers you an opportunity to open another one for 80 or 900 gems respectively, but be wary.
I tried to today on a rare chest because another card was 12,500 feathers, which I see as being worth 80 gems. Same would go for 500 or 850 black pearls.
So I picked the card that should have been the feathers, but the cards reshuffle and all I ended up getting was a mighty eagle. Irritating, but I suspect that Rovio added that just as another way to try and siphon gems from players.