Wizards Unite Green Books are new restricted section books added to the game recently. They are acquired through special events and not through other means yet.
Wizards Unite has only been out for a couple days, and there are a lot of questions about certain aspects of the game. A large question is about some of the books needed to enhance certain aspects within the game.
Wizards Unite Green Books: How to Earn Green Books
Currently, there is no other way to get the green books other than trying to find special events that give them out. This is likely to change due to the green books having a good deal of utility and not a lot of accessibility. There is a lot of discord because of this supply and demand problem and hopefully green books will be able to either be more widely found in the game, or their uses become more in line with how difficult they are to acquire.
So finish daily tasks or completing challenges inside Fortresses during events should reward you with Green Books.
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