PKHeX (20240112) Legality issue:
Shiny deerling from ORAS, when transferred to SV and switched seasonal forms turn illegal.
Deerling whose form stayed as Spring (legal, for comparison):
0585 ★ - Deerling - 2565E28F12A2.pk9
Deerling whose form was changed in SV (illegal, encounter type became invalid, memory)
0585-01 ★ - Deerling - 11D0C90A7F2F.pk90585-02 ★ - Deerling - 87B1DE229DDC.pk90585-03 ★ - Deerling - A50B4DFA5F78.pk9
The same issue is present in Sawsbuck. Spring forms are legal, other three forms are illegal.
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Event starters obtained from HOME are flagged as illegal but when checked they are flagged as legal.
0906 - Sprigatito - E3201FE864A5.pk90909 - Fuecoco - 8A1EFC980518.pk90912 - Quaxly - 763B4892D588.pk90585-02 ★ - Deerling - 87B1DE229DDC.pk9
None were genned through PKHeX, though the Deerling/Sawsbuck were obtained through a shiny hack on the 3DS.