Trying to follow other guides to earn this achievement was difficult, so I made my own.
It should be done on "Promenade of the Condemned", normal difficulty.
Just start and go right trying to reach the elevator at the end of the level, passing through those flying enemies as much as you can, to make them follow you.
IMPORTANT: Do not use traps or survival items, since they can easily kill them.
When you reach the end of the level and you are being followed by a ton of them, go up and down until you kill one. In this run I killed 5 with this method so it works.