This achievement can be done one of two ways or a combination of both.
But you have to get all the kill in one game.
Option 1 - Use the Storm Bow
Option 2 - Use traps such as the Death Ray
The easiest way by far is too get the "Storm" Bow as it can kill lots of Zombies very quickly and easily get you enough kills.
Below you will see guides for how to get the Regular bow and How to upgrade it to the "Storm Bow"
Storm Bow Upgrade Quest
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Wrath of the Ancients Bow (Regular Bow) Guide
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