This is one of the many glitches that can be encountered in Spyro: Enter the Dragonfly. In the 'slide' minigames, when Spyro accidentally slides into a drop off, he might end up stuck in an Unlimited Fall (oftentimes this causes the game to freeze).
In Spyro: A Hero's Tail, there was a glitch in Crocovile Swamp where the level didn't load correctly (most likely due to a disc read error) and Spyro fell straight through and kept falling. Also, the glitch also appears on the elevator to Cloudy Domain, the area can appear all black. Do not jump off the elevator, as Spyro will fall forever.
In The Legend of Spyro: The Eternal Night, a similar glitch caused by using Dark Spyro's 'flying' technique can lead to Spyro eternally falling outside the level, where you have no option but to restart the game.
|Swim in the air - Skip through the game - Double Jump - Dead Mode - Proxy Run - Proxy Jump - Collision Free - Unlimited Fall - Lost Gem - Fluffy|
|Dark Spyro - Unlimited Fall|