RESEARCH and DESTROY

I managed to get this in the Northern Frosts level when the area was only level one. One of the objectives will be to "Run'n'Gun to the Jetties" and get all 3 of your scientists into the ring of lights to progress the level. After reaching the location and ending your turn enemies will begin to spawn. In the water between 2 piers a Mummy, Ghost, Boogeyman and Zombie Runner will spawn. Throw your Gravity Distorter in a location where it will reach them all and then when it is the Supernatural's Turn and they all try to move they will be affected by the Gravity Distorter netting you the achievement.

Edit: After playing some more its clear the enemy spawn is somewhat random. I did notice that enemies tend to spawn in the same locations when you replay a mission, however. If you notice 4 unique Supernaturals spawn near each other and don't manage to get them all in the Gravity Distorter, try playing the level again (at the same Supernatural "Level" shown on the map) another time.