Help Skill Combo Problem

I am trying to create 2 new skills as a combo. I want the 1st skill to do decoy and give a buff for some seconds and the 2nd do shadow step when that buff is applied and remove that buff when the 2nd skill is used. (Example: i want to work as restoration and restoration impact skills with are judicator's skills.)

l2j gracia final.

(sorry for my bad english).

if you need more information let me know.