It looks like this:
That would make testUpgrade required for the shiny, and give the shiny a frequency of 10 with variation of 5.
- Make the shiny.
- Make a new resource to be used as a timer.
- Make the thing that you want to be the requirement.
- On that thing: make an on tick effect that makes the timer resource count down, an on tick effect that resets the timer and spawns the shiny if the timer resource is zero, and (optionally) an on earn: effect that sets the timer.
You should now have a shiny with a requirement!
Make sure not to use the frequency setting on the shiny.