When the series first came out, the Mane 6 was made in a pattern; Two Earth Ponies, Two Pegasi, Two Unicorns. But when Twilight became an Alicorn, it broke the pattern. When only one unicorn, they keep getting these "unofficial seventh members", like Starlight Glimmer.

This got me noticing the three major characters introduced in the Equestria Girls franchise represent the different pony kinds: Sunset Shimmer is really a unicorn, Flash Sentry is a pegasus in Equestria, and Timber Spruce could clearly be an earth pony.

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