Often, when activating certain triggers, for example hitting specific switches or lighting torches, the game freezes for a short moment, nullifying any input. In this period of time the Links can clip into any tile you want by using the acceleration of a C-Formation. However, due to the limited time, you can only bypass two tiles at best. If the Links are inside a wall when the game resumes, they will simply respawn next to it.
It is used in 1-2 to skip one small key and in 3-2 at the beginning.
1-3 has a lot of uses, but none of them are useful for a speedrun.