In my game (the DS port of Chrono Trigger) I spared Magus, but in the ending sequence, both he and Frog appeared–and Frog was cured! I had been told that sparing Magus automatically meant that Frog would not be cured in the end, and that the only way to cure Frog was to kill Magus when you have the opportunity to fight him a second time. But, like I said, Frog appeared in the ending sequence as a human man, and Magus wooshed by during the montage, so I got to have my cake and eat it too.
I have so far been unable to find any corroboration on the Internet or anywhere else that the ending I got, with both Magus alive and Frog turned back human, is supposed to exist at all. Is there anyone out there who also got this ending? I have my theories as to how it came about, but I want to know if anyone else has had this experience, and what it was that they did to bring it about.
Best Answer
This ending it's called in the wikia as Revenge for Cyrus
If you face Magus in Noth Cape with Frog on face to face battle, sparing him or killing him will result in this ending after defeating lavos.
Furthermore, killing or sparing him changes a little the final sequence but in both cases Frog becomes Glenn (human) again.