Chromatic Sphere "[@Spook":](/images/2459169#comment_9297869
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I wonder if it had anything to do with Rarity improving as a character. Not to say sShe was never a bad character to begin with, but I think she got better over time. (that Spike/Gabby episode not withstanding), not to mention she She was always stronger willed, like Applejack(who also improved, though not to the same extent as Rarity) and Rainbow Dash, and I think that's why those ships (RariDash and Appledash) overtook TwiDash.