Sword of the Necromancer

You will unlock this after the first time beating the necromancer with Tama. If you get stuck or have a hard time beating any boos or the floor itself, try to equip stuff that raises your strenght, because you benefit from these effects, even if you use another weapon. That means your main weapon should be scaling with strenght and not magic (like the necro sword) and should hit fast like lance, pike or Sabre or anything that you prefer the most. Hitting fast means you can melt down any boss lifepoints and makes every fight a joke, at least on easy.

Needless to say you should evade debuffs like 50% less attack power. If you chose this playstyle, you probably use all slots for boosting your stats and don't use necromancy that often. For the sake of other achievements, make sure to still revive each type of monster at least once and bring 5 to a white star at some point during the campaign.