Bonus Damage
Before we go deeper into the guide, I want to clarify the mystery of bonus damage first. So in general, there are 3 sources of bonus damage:
Element Property Additional Damage:
Currently Cafrisun Set , Sacrament and Enchant Fire give this bonus damage (there is probably a typo in Sacrament and Enchant Fire description because their property damage act the same as Cafrisun). This adds an additional hit every time you auto attack, and each element add one additional hit. This damage doesn't get added to your normal attack and skills.
Element Property Attack:
Arde Dagger, Karacha Dagger, Ledas Shield, etc. offers this bonus damage. This gets added into everything, your normal attack, your additional hit caused by Element Property Additional Damage, and your skills. Multi hit skills has each hit added with bonus attack.
Additional Damage:
You can see this bonus from Blessing and part of Sacrament. This bonus acts the same as Element Property Attack. It gets added to your normal attack, additional hit and your skills. Multi hit skills has each hit added with bonus attack.