the fastest way to kill zombie champion is probably with a chaotic rapier.

 

drops of the zombie champion:

 

                                           super rare: Primal rapier

 

                                          rare: pvm armours

 

                                         uncommon: Berserker ring (i), warrior ring (i), archers ring (i), seers ring (i).

 

                                         common: sanfew serum (4), berserker ring, archers ring, warrior ring, seers ring