doesn't really matter now, i found a fe6 save with all secret characters, but ftw, the save has 2 of each secret character, and idoun is there as a dark druid xD
oh and if i have 2 echidnas, after i beat the game and go to trail map with that save, will there still be 2 echidnas or will it be filtered out? i think i did that before, but i want to make sure i'm rite

EDIT: I think i have a explanation on why idoun did not transform. It might have been because I had a idoun in my party (note: i didnt take her along the final chapter).
if anyone has any theories, they are welcome.