Secret Course 19
From the Super Mario Wiki
Secret Course 19 is the nineteenth secret course that appears in the Remix 10 mode of Super Mario Run. This secret course takes place in an underground area.
This course starts with the player dropping in from a Warp Pipe and leads into a hallway with many Dry Bones that the player can jump on. There are also four Fishing Boos on the way. Three of the Bonus Medals are found dangling from the Fishing Boos' rods while a Super Mushroom dangles from the fourth Fishing Boo. Another Bonus Medal is found by jumping from the second Dry Bones while the fifth and final Bonus Medal is found by jumping off the last Dry Bones right before the Warp Pipe to exit the course.