Bad Export for You: The Japanese release of the first two games was plagued by numerous issues, including numerous glitches, a nearly uncontrollable camera, and most inexplicably, signs scattered literally everywhere that caused "helpful" tips to pop up whenever they were hit with Spyro's flame, accidentally or otherwise. Understandably, the first two games did not do well in Japan, and as a result Year of the Dragon never made it there.
Channel Hop: Went from Universal Interactive for the first few games, then to Vivendi Universal (the name they assumed before the NBC merger, after having merged with a French conglomerate), who then organized Spyro under video game stalwart Sierra, who they had bought a few years before. And after that (after most of Universal had become part of GE, then Comcast), the remains of VU/Sierra went to Activision.
Executive Meddling: Heck, this whole franchise was built around this trope. Originally, Sony of America wanted to create a "kid friendly game and character for the PlayStation" (considering the games at the time were... ratheradultandteen oriented), hence the creation of the franchise, in which Insomniac never even had the full rights of in the first place, which resulted after Year of the Dragon's release that the franchise was sold and then became a Franchise Zombie until purchased by Sierra, who being way past their time ended up being bought out by Activision along with the rest of the Universal/Vivendi group.
The Other Darrin: In the first game Spyro was voiced by Carlos Alazraqui, then by Tom Kenny for the rest of the PSOne era plus Enter the Dragonfly, Jess Harnell for A Hero's Tail and Shadow Legacy, then Elijah Wood for the Legend games, and finally Josh Keaton in Skylanders. Within The Legend of Spyro trilogy, Sparx changes voices in every game (David Spade, Billy West, and Wayne Brady), and Cynder goes from being Cree Summer to Mae Whitman, then Christina Ricci, and finally Tobie LaSalandra in Skylanders.
All of the Spyro titles featured at least one cast change, with the exception of Enter The Dragonfly which kept all of it's characters' voice actors from Year Of The Dragon. All of the cast were replaced in A Hero's Tail except for Andre Soqliuzzo (though he voices Sparx completely differently anyway).
What Could Have Been: Elora was meant to be originally a centaur instead of a faun, and Sgt. Byrd was a pig instead of a penguin. Sheila had horns, wore a t-shirt, and had boxing gloves in early concept arts. There was going to be a MMORPG based off the Legend Of Spyro series but it got scrapped for Skylanders. Elora was meant to appear in Attack of the Rhynocs and Season Of Ice but was scrapped due to time constraints.
There were plans for an Agent 9 spinoff. One project was a complete reboot, where Agent 9 was called "Prime 8" and had a realistic redesign. The other was more faithful to the original.
Spyro was originally green and his name was "Pete" at one point in development.
The last page of the manual for Spyro The Dragon shows what seems to be an adult version of Spyro◊. It is unknown if he was supposed to appear as such in the game itself or a sequel but no other artworks featuring that concept seem to have been made.