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Ok, well, one last non plot related thing
In the basement of this place after you get the red key card (which gets us to the last rooms) you can come back to the beginning and in the basement there's this patch of grass with only level 100 Blisseys here in case you need to patch up your final mons to level 100
Sounds nice, but you can also infinite rare candies from any pokemon center (admittedly, it's a secret way) so this is kind of useless