Evoland Legendary Edition

Oddly, this achievement actually takes place in the "Haunted Forest". The "Ghost Forest" is apparently the name of the music track for this area.
After you clear the Haunted Forest in the Past, you can walk through it on the overworld and enter from either side. To clean up this achievement, I went in the front entrance, went left to a group of 4 zombies, cleared them out and left. It took 2-3 runs of this strategy to pop the achievement after the area was previously cleared.

Ghost Forest is in Evoland 2. Place where you need to fight the Ghosts and then the Blue Cel looking guy. I only had to go into it twice and on my 2nd run it was just 3 Zeds I needed to take down for the achievement.