You can use this system to add demage:
First you need create or copy some object ability with demage bonus and add 2 more levels, now the OBJECT ability have 3 levels, change the value of the bonus demage in all levels, ex: 20, 40, 60.
Change the name to AddDemage, Now see the system (picture)
Note: you can use other name, value and lvls.
Tell me if you not understand someting about the system or the spanish (XD)