For any%, you need 4 green kinstones for the Magical Boomerang sidequest:
There are a couple options for obtaining this set of kinstones that with varying levels of difficulty.
This is the most beginner friendly route for runners who do not use Armos Clip. This route requires 3 save and quits total, making it the slowest option.
Runners that use Armos Clip have a couple options. The first option is to perform the first two manips in the "No Armos Clip Route" above and obtain a G< from Armos Clip. This saves one save and quit over the beginner route.
The other option is the use the Quadruple Kinstone Swamp Manip by Vlack. This can potentially save 2 save and quits and a couple seconds after Armos Clip. Getting the third and fourth kinstones from this manip can be very inconsistent. However, if you get the first 2, you can easily continue the run and obtain the others through other means. Below outlines the steps you should take if you don't obtain all 4 kinstones:
Obtain Only The First 2 Kinstones
Obtain Only The First 3 Kinstones
If all 4 kinstones are obtained, you do not need to manipulate any drops from the Armos after clipping.