RTA Guide/Rematch with Koopa the Quick
Rematch with Koopa the Quick is the third mission of Tiny-Huge Island.
Standard Shell Route
Note: this video shows the proper lag reduction for the ending. Make sure to stay in Mariocam C-Down, and keep the camera facing the out-of-bounds area.
This video explains the RNG that affects how fast Koopa the Quick finishes the race.
Mountain Clip Route
This route guarantees that no balls will get in Koopa's way during the race, so it might give you faster times on average. This is explained in more detail in the above video.