This achievement has you get 50 kills with the slam ability, which is quite fun. The slam can be found at the Earthscar Ark
in the Torn Plains, a ways East of Wellspring. Once you have it the best place to get kills is, as per usual, mutie nests. There's just so many of them that spawn at the same time, especially if you destroy a couple eggs at first. Done right, you could get 50 kills in 5 slams or less. The vortex upgrade is very useful for maximizing efficiency as well.
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