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Yes, I agree. They probably reformed as there wouldn't be another way to fix the uncorrupted gems (most of the fandom wanted that)... And their new powers (apparently, a Diamond becoming good means their power becomes less destructive) ended up being pretty useful (well, Yellow and White's powers, Blue's basically are the Gem equivalent of getting high).
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[@Brass Beau":](/forums/pony/topics/mlp-g5-discussion-and-speculation-thread?post_id=4981480#post_4981480
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Probably like Sombra, Storm King and (in my opinion) Chrysalis: Irredeemably evil, but charismatic.