This is level 52 of the Main tunnel.
Using the Runner in this level requires you to maneuver between the platforms from the gaps. Since not all crumbling tiles are connected, so you don't have to afraid of toppling the crumbling tiles. Dodge left/right to avoid the gaps, and walk onto the crumbling tiles when necessary. Since the rectangular paths made of crumbling tiles are quite long, so you may need to a long jump in order to reach the end.
As for the Skater, run as fast as you can, and gain as much speed as you can. Then, do long jumps, and land on anywhere with normal tiles and crumbling tiles (not holes!). Repeat for a few times and you will reach the next level.