The Heaven Tavern is used to obtain new heroes for your formation.
Shuffle: When you click shuffle, the 5 cards will be "shuffled" (see odds below) and flipped over. You can then choose a card and it will be one of the 5 that were shown before shuffling, the card you pick will be available for you to place in your formation.
Refresh: For a certain amount of credits (Based on your level, adds around 1k cost per level), this button will give you a new set of 5 cards to play. every 2 hours you obtain a free refresh (done automatically, so don't forget to check the tavern periodically for those purple/gold cards)
Auto Refresh: Available for VIP4+ players, this will press refresh for you until a purple or gold card is in the deck
You would think that the odds of obtaining a card in the shown set of 5 is 1 in 5, however this is not true. The deck is actually just an illusion and the card(up to 3) that you will actually receive (or not receive) is predetermined. The odds of flipping over a hero when it is in the deck you play is probably on par with obtaining a gold rune from the rune temple. It seems to be around 1.25% - 2.5% chance of flipping over the gold card.
Due to the odds being unfairly stacked against you instead of being 1 in 5 for obtaining the card you want, every time a purple or gold card is in the deck you will receive, according to the game developers, a number of spirits based on your level (10 spirits is highest known value). Clicking on the redeem button will allow you to purchase certain heroes instead of having to flip over a card. The price ranges from 500 for a purple hero to 800+ for a gold hero. (Plan on spending millions and millions and millions and millions of credits to obtain those gold heroes).
Name Title Golden/Puple Spirit cost Saffron Mad Chemist Purple 500 Cianna The Deceiver Purple 500 Valla The Berserker Purple 500 Alexa Fallen Angel Purple 500 Calvin Will Breaker Purple 500 Dawnbringer Headman's Sun Golden 800 Rhize Champion Golden 1000 Shayd The Deathsinger Golden 1200 Smoulder The Rogue Golden 1200 Adamanti Blades Master Golden 1500 Bloodstorm Revenant Golden 1800