What percentage of possibilities does King Rock cause a flinch if I use the Move with a different effect?

I Using Meloetta Pokemon with Serene Grace and hold King Rock ( 10.2 = 20%) and I use the following move :

For Example :

Shadaw Ball-> give demage amount 80 and chance to reduce SP. Deff by : 20% ( 20.2 = 40%) withserene grace

And the question is :1.what percentage of possibilities does King Rock cause a flinch? 40% reduceSP.Deff& 20% chance to causeflinch?2. if Shadaw Ball is an active side effect, is it possible that the effects of King Rock are also active for making Flinch?and ifYes3.what percentage of possibilities does King Rock cause a flinch?

thanks!

Pleaselog inorregisterto add a comment.

King’s Rock has a 10% chance of causing a flinch, and that is its only effect – so the chance of a move lowering a stat or causing a status ailment won’t be affected by the item.King’s Rock only effects moves that do not already have a flinch rate, so it would not stack with moves like Iron Head, for example. It does, however, stack with Serene Grace. So a Pokemon with Serene Grace holding a King’s Rock has a 20% chance of causing the opponent to flinch when using a move without a flinch rate.

Hope this helped.