i have 2 files - 20 lvl destr and 25 lvl gunslinger...i beet everyone with destr AFTER playing gunslinger (and eventually getting him magic instead of melee-damage skillls) after about 6 kills i got the badge) the shadow is easier than the doctor (previous boss) it's much like omen...i also played the assassin but never got past 1st boss (and wasted around 3 hours on the paladin) i think the damage has to do with the skill dependant on speed (right before coup de grace) but you still don't have shadow blend to make it hit 6k on the shadow)
strange thing - beat the shadow 3 times already and no badge...the hardest boss here for me was ignition (1st battle zone4) and the others were pretty much easy after 1 fight (i lose the first one and win the second fight) gunslinger lvl 25 full paladin set...use the combat medic and the assassin - strange thing she does her shadow blend and becomes some sort of killing machine - duno how to that with an assassin...4/5 good game (4 because it's short)