Every game you play, you win free coins, even if you lose!
Winning a Game
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Win a game and you will rewarded with a number of coins.

• Win vs 1 Bot = 3 coins
• Win vs 2 Bots = 7 coins
• Win vs 3 Bots = 16 coins
• Win vs 1 Human = 5 coins
• Win vs 2 Humans = 12 coins
• Win vs 3 Humans = 20 coins

Finding a Gem
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Whenever you win a game there is a chance that instead of coins, you could find a rare Green gem, or an even more valuable, ultra-rare Red gem (worth 30 green gems). Gems can be used to trade for individual cards direct from the Library.
Losing a Game
If you lose a game, regardless of its type or number of players, you will always win a coin.
Twilight Dragon
This creature is deceptively dangerous. For a relatively low cost, this creature has high enough hit it is difficult to kill easily, and can do a surprising amount of damage while your opponent scrambles to deal with it. 
A good card to draw your opponent's easy kill options (fatal blow etc.) leaving room for even more dangerous options later to emerge with no answer...
Tax Collector
Consider your Capital to be like your credit score; destroy anyone who prevents you from getting it higher... Or, do the American thing, and ask; "How can I make other people do it for me?".