"D4 damager" - in Dungeons & Dragons (D&D), each character class has a different die for attacks from damage. The four sided die (D4) is the damage die for the Wizard class. So, a "D4 Damager" is a wizard.
"Renegade Master" - a Samurai without a master is a renegade (ronin). one of McKenzie's meanings here could be "renegade master" not in the sense "a master who is a renegade", but in the sense "the master of those who are renegades".
Putting those 2 things together, we're back once again, for the wizard who is the master of renegades.