This level is a new type of level called a spiral level.
For this level, we highly recommend using the Skater as you can clear the level in one jump. This of course makes sense since it is one of the shortest levels in the game, if not the shortest. In fact, you can see the end of the level from the end of Level 19.
When you start, change gravity to the right. Then when you get to the crumbling tile, jump. Then immediately move over to the right. An alternate route which only requires one extra jump is to not move side to side at all and jump in a straight line. The Skater's speed gives you that ability to jump such a long distance.
But with the Runner and Lizard, there's a different technique. Since their shorter jumps cannot bring you across the large gaps that the Skater can, you must simply follow the tunnel in a spiral by continuously moving to the right. Move right immediately once a tile appears on the right to you and run around the tunnel to the end or you may not be able to avoid the gaps without jumping (which would most likely fail unless it is the final jump). You can also do this: Jump, move right, and repeat. You may lose the crumbling tiles, but they're a chain of one-tile wide platforms, and minus them should cause no problems.
- This level references Level 20 in Run 1. Some levels of the Main Tunnel in Run 3 reuse levels from Run 1.