[Scripting Question] How can i add a item that increases shiny rate temporarily?

[Kemuel]

My english is bad, but i am going to try without the translator, i want to add a "Shiny Rune" and it increases the chance of encountering a Shiny Pokémon for like, 30 minutes. How can i do that? I can code it like an event(e.g Berry Trees)? with pbSetEventTime and CooledDown switch?

 

[HeartyAlexii]

the i in the 2nd sentence should be moved over on word