Ride cancelling

When Mario gets off of a shell, the game sends a "signal" that the shell uses to decide that it should unload. The "getting off a shell" signal overrides other signals, so if the player gets off a shell at the same time as collecting a coin, but the stop riding signal will prevent the coin from actually unloading.

This process can be repeated by using a cloned shell, which allows for the shell to be reused multiple times.