Among the most coveted magical items in Clash of Clans is the Universal Book, and if you want to know what it is used for then be sure to read this Mobailgamer post.
Role of the Universal Book in Clash of Clans
The function of the universal book is basically to complete the improvement processes, skipping the timers of both the main village and those of the builder base.
This book can be purchased from the merchant and very rarely from the clan game shop, so it is quite valuable and should not be wasted. It is recommended to use especially in improvements of the main village in which the time is very long.