Well Zand when making your decision please take into account my How to keep everyone happy post where I describe how Mjarin remains the Head and Moagim the Leveller with little damage to Myth I or II or III plot.
Okay lets see if we can make evryone happy-ish.
Mjarin, former hero of the wind age, becomes corrupted by the leveller, because the Leveller can't posses him because he's still alive, he the joins Warlocks, becomes leader.
When the Levellers power reaches its peak, he was supposed to posses Mjarin, but Mjarin isn't so hot on being killed and possesed, so he makes a deal, I give you Moagim, you teach me Magic. so he ressurects Moagim, maybe he found the body and head and attachted someone elses arms or something.Moagim teaches him the magics, however Mjarin plots against Moagim, because he is not the Leveller he seeks conquest not death. This explains his un-Levellerish actions and makes Myth III make allot more sense really.
So Basically, Moagim WAS the Leveller, Mjarin pretended to be on the Levellers side, pretended to be on the Cath Bruigs side, but as usual was only on his own side.
-zeph