Working on battle sound fx led to me mucking around in the game, and even after many years and playthroughs, I still made a few discoveries.
If you return to the Middle Ages after defeating Magus:
• the people of Guardia Castle express their gratitude for helping them win the human-mystic war, and if you bring Frog, you get special dialogue.
• over in Manoria Cathedral, there's a nun (real, not fake) who gives you encouraging words.
Pardon me if this was posted before, I just wanted to share with all. I thought I had known all the details of the game, so it was really cool to find something new.
Other points of interest which are probably known:
• Singing Mountain (it's unfortunate this wasn't included, it always bothered me that the east side of the continent in prehistory was empty)
• the unused dungeon under the Blue Pyramid
• the unused cutscene accessed via Schala's room
• You can introduce your party members to Chrono's Mom. If you visit her while Chrono is gone, your characters lie about the situation, and Bottom of the Night plays.
If you've got more easter eggs or details to discuss, feel free to post em. This thread can be a repository for any and all obscure content.