Book of Astrology (BoA as acronym) is an item you can get from the Shop, by archiving Goals, finishing quests or killing dongeon boss. You can use this item at the Tavern to have increased chances to choose from better heroes. While this got an increased chance, it doesn't neccessary means you WILL find a red, orange or even a purple hero. But in most cases you can see purples, at least.
By using 20 books of astrology in Tavern you will gain by a Orange Hero Card.
|Book of Astrology|