Yay me! I was playing the GBA version of FF4, and to my joy I actually beat Rubicant!
Anyway, just before you go to the moon to defeat Zemus, my game said "You can now change characters at the Mysidia Tower (or Prayer Place or whatever)" and so when I arrived there, a little sidequest was waiting for me!
Tell me, could you change characters in the NES version, and can you do the Mysidia sidequest, or is it a unique thing to the GBA version?