Guile = Magil = Magus?
Magus’s current whereabouts in the Chrono series are unknown; he was last seen departing to 12000 B.C. to search for Schala. In Radical Dreamers, he came back to the modern era and disguised himself as Magil to watch over Kid. In Chrono Cross, he was meant to be a disguised character named Guile. However, the developers felt it would be too hard to represent his story amongst all the other characters, and Guile’s backstory was removed. Magus is mentioned once in Chrono Cross in the letter to Kid from Lucca; he is called Janus, his real name. Thanks to Chrono Trigger DS, there is a possibility that Guile is a form of Magus; check this page.