Freeroamer
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You're also looking at the issue a little one-dimensionally in that you're just focusing on whether it gained new answers. Yes Xern gained a moderately viable new check in Magearna, however SM has also seen the prevalence of Dark types rise, which is obviously a positive factor for Xern given that it beats both Arceus-Dark and Yveltal under normal conditions provided it's played reasonably well. It's also gained a new set in it's Z set, which increases it's versatility and threat at a teambuilder level, because a lot of Xern checks that can help vs standard Geomancy can fall a little cold against the Z set. Xerneas is still one of the most limiting factors on teambuilding in Ubers without a doubt and manages to combine that offensive threat with reasonable defensive utility, and as such fully deserves it's place in S Rank.