So this achievement requires you to build the Raven Lord Melee Weapons and get 100 kills each of them in 1 game! Its 4 different thulian weapons, The Scythe (Fang of An'heist), The Hammer (Fist of Tal'rek), The Shield (Roar of Sang'ket) and The Broken Flail (Talon of Lu'roth) and all variants must be built in the same game. You do not need to build all of them yourself, as soon as they're all built everyone in the game you just need to get 100 kills with each weapons. You don't need to upgrade the weapons
, but in my opinion you should because it's very easy to upgrade them if you know what to do and they're all get really powerfull! Once you have all upgraded or standard Thulian variants of the weapons just kill 100 zombies with the melee weapons in the same game, one by one and you should get the achievement! If you upgrade all of the Raven Lord Weapons in one game by yourself you will get a hidden character challenge!
My tutorial/guide video for all weapons (How to obtain & upgrade them):