How To Unlock: Use every type of melee weapon on a zombie.
It is not required to kill them, hitting them will suffice. As all other multi-playthrough achievements, there have been reports of it not unlocking when it should. Again, try to contain the requirements in one playthrough, to be on the safe side. Take note of the following items and ensure you find these while doing the relevant missions/cases. Unique items:
■Giant Pink Chainsaw - 'Here Comes The Groom' side mission
■Katana - Case 4-1
■Magician's sword - 'The World's Most Dangerous Trick' side mission
■Military Case - Starting from Case 5, hard to miss boxes though.
■Trophy - 'Two for Company' side mission.