Morgan and Owain started as a Level 10 Cleric and Myrmidon, respectivly. After playing the free DLC map 3 times with only Morgan and Owain paired up they Became Level 10 Tacticians. Now I am leveling them up as Dark Mages, then Sorcerers.
Remember, Tactitains get 50% XP Bonus when Paired Up. So Avatar's Children should become Tacticians first, then they can level they class you REALLY want that much faster. And because Avatar children can be almost any class, they can grind for skill a lot faster than anyone else.
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Level 10 Dark Mage Owain and Level 7 Dark Mage Morgan do a challenge battle at the Milla Tree. The monsters were all promoted units. Morgan took was in the lead paired with Owain and all else fell back. MorganActually Killed every monster on the map by just sitting in one spot and waiting to be attacked. She went from Lv. 7 to Lv. 20 in one battle.
In the course of one afternoon Morgan went from a Level 10 Cleric (how she was generated) to a Level 10 Tactician. To a Level 20 Dark Mage!!!
I did NOT save because my Main Team need the XP WAY MORE than she does. I am going to remove the XP ability from them to slow them down. This is something to remember for Lunatic Mode though.