To start off you need the Heart of Chao, of course, and a non-rare mag, with all levels over 35. This was a lot easier on the DC game because there was no rare mag evolution on its own. If you do make your mag into an EPII rare mag it wont work with the cell, i found that out the hard way . The easiest way to raise a mag to be a Chao is to first raise all of the stats to level 20 so you mag is at a total level of 80. Now heres the tricky part that can get confusing to some. When a mag is level 100 or above it will turn into a rare mag if the sum of 2 stats is equal to the sum of the two remaining stats. To avoid this you have to raise the stats one pair at a time, And in my opinion its best to raise each stat at one at a time.

Now I will explain how to do this section ID by section ID, since the rare mag conditions are diff for each. All of the ID's begin by raising all stats to level 20 each, so that the total level is 80. Then continue by your section ID.