It's because Darumaka-1's altform (required 1) doesn't match the current PKM's altform (actual 2)
PKHeX's legality check checks for matching forms (since in prior games, pokemon didn't change their altform)
edit: now fixed, thanks for reporting (I had another MrMime case passed along by someone else):
https://github.com/kwsch/PKHeX/commit/913d2773bffe0b665eb6f9e65d99d95515da7593