So, hopefully Starlight Glimmer will be making a return later this season, at which point we'll probably find out more about her goals, motivations, etc.

(I fully retain the right to dismiss these if they turn her from a compelling character into a two-dimensional villain).

Until then, however, what do you think she was trying to achieve? While she was pretty excited to have a Princess on her side, there's no telling how long Our Town was there and we don't know how Starlight actually recruited ponies to her cause. She met Double Diamond in the mountains not far from where the town was founded, and the Mane Six came to her... so do you think she had plans of converting all of Equestria? Was she gathering strength before trying to Equalize all other ponies? Or did she plan on staying where she was, prior to Twilight (and the opportunities of having a sympathetic princess) arrived?

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so do you think she had plans of converting all of Equestria?

Without doubt. When leading them to the cave she said that one day, she hoped ALL of Equestria would go there to get equalized.

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I think that she think she doing is the right thing. For main characters cutie mark being the most important to get for what ever reason maybe to gain immunity from the rainbow magic. But I do believe a third party is involve in this and Starlight is just a pawn.