Instructions
Return to Ryllus and enter the Vegeta Jungle stage. Plant the fruit bomb in the first area, uproot it, then bomb the wall in front of you.
Plant another bomb, then turn around and bomb the wall directly behind you at the start of this stage. The wall is hidden and looks like the side of the mountain. Bombing the wall in front of you triggers the rear wall to be breakable.
Enter the cave and jump up onto the ledge. The Sludge Mk. 9 Boots should be tucked away there.