The only piece of ‘evidence’ I can bring to support my pronunciation is that Magus has gone by the name Gil and Magil in Radical Dreamers and Chrono Cross, respectively. (Granted, the one in Chrono Cross isn’t Magus himself, but was supposed to be when they named the character, so it still counts.) Gil, from Radical Dreamers, came first, and really only has one way to be pronounced, that of ‘gill’, like those on a fish. Now, Magil you could pronounce “may-jill’, but as the name is clearly building off of Gil, that no longer makes sense. The end result is that Magil is pronounced either ‘Mah-gill’ or ‘Mag-ill’, there isn’t really much difference there. Again, as Magil is an expy for Magus, it can be assumed that the names are pronounced the similarly; thus, Magus is pronounced Mah-gus, or Mag-us.