Frog Softlock Explanation

Summary:

After receiving a reward from Cremia, there is a cutscene status flag that does not clear correctly.  (This has been fixed on the English version of the game.)  Normally this isn't an issue, as watching any cutscene that also uses this flag will clear it (and many cutscenes use it).  However, at the start of the frog song cutscene, the game checks this flag, and if it is set the game will not load certain data required to make the cutscene play correctly.  So, going straight from Cremia's reward to the Don Gero HP will result in this softlock (this is entirely possible in casual gameplay).  The initial debug 100% route went to this HP shortly after getting Romani Mask, and did not watch any cs that would clear it along the way.  Future routes will account for this oddity.

More Detail:

All addresses will be JP 1.0 unless specified otherwise.

There is a flag at 801D0E60 (byte; 801D1070 J1.1/801D66B0 Eng) which has default value 00, and is set to 01 during many cutscenes.  From seeing a few places where it's used, my best guess at its purpose (emphasis on guess) is to keep unnecessary code from executing during cutscenes.

When receiving a reward item (this can be Romani mask or rupees) from Cremia, this flag is not unset on leaving the area.  When receiving a hug or failing the minigame things function normally.

After completing the text of the frogs in MV spring, there is code at 8019CEF0 which checks this flag.  If the flag is nonzero, the function branches and skips some code.  That code writes to 801FD570-801FD587, and the values it writes there are necessary for the cutscene to play properly.  The code that's responsible for this check is possibly generic, since there's no good reason for the frog cs to check for it.  Or the check could have been left in from a previous version of the code, since normally it's not harmful for it to be there.