Master Exploder is by far the weakest of all opponents on the Arena. He suffers from many problems such as subpar defense, lack of mobility, low AP and his offense is not really impressive either. He really could use few more feats like for example Thick Skull, Conditioning, Sprint or Premeditation. HE grenades are also probably the weakest grenade type possible, maybe give him Frag Grenades instead.
Also it would make sense if Zap had High-Technicalities Feat.