Board Thread:Questions and Answers/@comment-172.6.246.2-20141116154013/@comment-27508440-20150801220009

You cannot combine spheres of the same type.

e..g. heresy orb and evil shard (both are bb boosting spheres, therefore, cannot be combined)

Note: Although Heresy Orb adds 15% to each parameter (stat), it says it fills 25% of bb gauge faster first, making it a bb boost sphere

legwand and legwand ( cannot be combined, both are status up sheres)

Conclusion:

ex sacred jewel and evil shard for double sphere effects.