For this achievement you need a
predator bow and the
"Enhanced Predator Bow" skill in the hunter skilltree. Travel back to Siwa because here can you find the weakest enemies. Use your eagle to find and mark an enemy which is over 60 meters away. Use your predator bow and hold
after you shoot the arrow until the arrow hit the enemy. You can control / steer the arrow with your
stick if you want (Fleeing enemies)
Note from Comment:
Don't be *TOO* far away when you fire the arrow as they don't seem to travel too much over 60M in the first place - I was 80M away and it fell short, so I moved to 65M and it worked fine