During the G4 era, a portion of the MLP fanbase was made up of people called "Bronies." You may of heard of them.
These people were (usually) primarily fans of the cartoon, Friendship is Magic, where 6 fun horses have adventures in a fantasy pony land. It's cute!
However, as is often true of the MLP toyline, G4 toys often took design liberties without regards to the canon of the franchise's other media ventures.
Some ponies from the show were changed to become almost unrecognizable as toys for reasons we may never know (corporate decision).
The much maligned pink Princess Celestia toys are one such example. For quite some time, Hasbro represented a pony with a white coat in the show as toys with a pink bodies.
Her sister, Princess Luna, did not fare much better. She is portrayed as having a dark indigo color in the show, but she had a long struggle to have any toy releases that weren't purple.
Ponies from the show also released as toys with differing names, and some toy ponies were entirely unique creations!
Therefore, there exist ponies exclusive to the toyline that never make it to the show (and vice versa).
Princess Gold Lily and Princess Sterling are two such ponies. They originally released in two-packs alongside Fluttershy and Pinkie Pie respectively, whom they had to share one comb with.
While obscured in their packaging at the thrift store, I found them to be peculiar, initially thinking that they were fakies.
Princess Gold Lily's pink wings and bright yellow body in particular are unusual, and their bright hair colors seem to have been picked with little reason.
Their cutie marks are also strange-- very vague, small, and printed in only one color.
But fakies, they were not. Just strange officially licensed releases.
These two toyline-only princess captivated a few in the fandom. The dedicated fans speculated about possible characters behind these ponies:
But nothing so exciting happened. They were weird plastic horses with names, and that was it.