Yelawolf is describing the torment he is receiving from the darkness. Perhaps it is evil itself, or an alter ego trying to get Yelawolf to do these evil things.
I believe it is something like a dark passenger inside him that wants him to be evil. The darkness that resides in Yelawolf wants him to be a monster. The darkness wants him to use a blade (a machete was talked about earlier in the song). The darkness wants to make Yelawolf to go crazy and into a rage.
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