Choose the map GoatZ before outbreak.
From the spawn turn right and hop over the rocks, if you have the Gravity or Flappy Goat Mutator you should easily make the small island where the Achievement can be obtained. Once you reach the island go up to one of the humans, use
and begin dragging the poor soul up the ramp where the cauldron is. Once at the top, drop him into the cauldron and the achievement will unlock.
5:00 in the video