Board Thread:Questions and Answers/@comment-99.13.228.129-20150721203518/@comment-26021614-20150725092305

The one he's talking about is Fury Core.

Demon Core, Fury Core, Alzeon Pearl, True Ore, Heresy Orb, Sacred Crystal, etc.

These great BB boost class spheres are all one time obtains so it's better not to look for "the best one" but mix it up and equip according to the needs of your unit. Fury Core will take you probably two years (or tons of gems) to obtain due to its requirement in arena of 3,303,000 points, and by that time you will most likely see so many updates that it won't even be the best BB booster out there anymore; there will be so many changes to the game that it is unpredictable what you will need for your suiting. Aim for easier to obtain spheres such as Heresy Orb or Sacred Crystal (when raid class 5 is released) instead. And mix it up; if you have a great BB spam leader such as Feeva or Zelnite you most likely won't even need these spheres, even for tougher bosses.