Recently acquired data disproves this theory, Lion is a Fusion. We appreciate the attempt.
|Lion is a Fusion|
|Title||Lion is a Fusion|
|Date of Publication||August 6th, 2016|
Rose was never able to heal a corrupted Gem, but it is possible, even likely, that she was able to partially heal a corrupted Gem to an extent similar to that Steven was able to achieve with Centipeetle Mother. Then she fused the partially healed Gem with Greg's cat, perhaps in the hopes that the cat would help stabilize the Gem. How she managed to do that I have no idea. However fusing Gems with organic beings has been shown to be possible, for example Stevonnie, and possibly Steven (Steven is a Fusion).
The resulting fusion would have many of the characteristics of a cat, and many of the characteristics of the Gem. It would be larger and more powerful than a domestic cat, and would have all the Gem's abilities and magic. This is a fair description of Lion.
Also, the fact that Lion is male, while Gems are all female, could be explained if Greg's cat were male.
To me the most likely Gem that Rose might have used would have been a corrupted Pink Diamond. This seems likely because Lion's Gem powers seem to exceed those of any other Gem, especially his ability to teleport.
In "Off Colors", Lars was resurrected by Steven, turning him pink and giving him a pocket dimension that connects to Lion's. This indicates that Lion was an ordinary lion who was resurrected by Rose Quartz.