What exactly are you referring to? I see nothing in the Paragon Market containing either "NPC" or "transformation" (I assume you misspelled that in your post and subject line).
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StainedGlassScarlet - L50 Spines/Inv Scrapper | Badges: 1,396
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I believe that's the category for NPC costume powers like the temporary ones we get at Halloween but you have access to them permanently. Last I heard they were pulled from the market, maybe they had a conflict with the Halloween versions.
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What is the "NPC Tranformation" in the Paragon Market?