the shiny stone?
ok, its a little bit hard to explain, but this will help you:
first: go to the skidoo ranch at route 12, then you go to one of the awoken skiddos and press a. you will now hop on his back and will be able to ride him. then , head to the north and you will find three ledges skidoo can jump over. jump over them and you will see a poke ball with a shiny stone
hope I helped:)
source: experience and this this detailed description with pictured