Sum Viewer
You should get it once you bounce up the mushroom and go through the tiny tunnel. Are you sure you don’t have credit already? Check your achieves panel.
If you don’t have credit, roam around everywhere you can get to on that ledge and go back and forth through the tunnel. I took a friend to get it some time in the last month and it triggered for her right away.
There is a very specific point you have to pass by to get it I think, I had to run around up there a bit to get it to trigger for me back in the day.