The Witcher 3: Wild Hunt
78 Achievements
100-120h
Environmentally Unfriendly
Kill 50 opponents using the environment (e.g. swamp gas, insects or objects).
53.8%
How to unlock the Environmentally Unfriendly achievement in The Witcher 3: Wild Hunt - Definitive Guide
O for oVR
TrueAchievements
TrueAchievements
dylan is white
TrueAchievements
TrueAchievements
This is in Velen, south east of the map. You go here for a main quest. Just go around in the red circles and you'll find drowners.
Small circle = 4 drowners
Big circle = 3+ (some spawn near swamp gas, some don't)
This is in White Orchard, North of the map. You go here for a main quest as well.
You can find 6+ here near swamp gas, just roam around.
Those were the only two places I went, but I'm sure there are better spots out there.
So go there, lure some drowners near the swamp gas, and then Igni (or fire bomb, but Igni is easier). Simple as that. After you kill them, leave the area and come back.
Shadow XBL
TrueAchievements
TrueAchievements
The 1.04 patch MIGHT have killed the previous solution, but it's still here just in case.
for an instant kill which seems to count, once done to as many harpies as I could in area (some can be too high up to get their attention coming after you), then fast travelled to Vizima and back so they'd respawn to repeat. You have to be quick in pressing the 
Diddlemyloins
TrueTrophies
TrueTrophies
PainOfDemise, PowerPyx
There are plenty of opportunities to obtain this trophy throughout the game. Igniting swamp gas, blowing up explosive barrels near opponents (and hope they die), destroy a bees nest near damaged enemies, or cast Aard on your opponents and knock them down, then walk up towards them and press 
while they are on their back for an instant kill, which will count. We found this the easiest method to obtain the trophy. This also works especially well on any bandit that you come across that is riding a horse, as they instantly fall on their back when blown off.
If you are to use any of the environmental objects, be sure you damage your opponents first, so that they actually die when you use the objects to try and kill them. After you get 50 kills due to using the environment, the trophy will unlock.
You will also get lots of environmental kills automatically during the Battle of Kaer Morhen. There are meteorites falling from the sky and barrels exploding without you doing anything. You will get the majority of required kills automatically during the battle. If you are lucky the trophy will unlock during the Battle of Kaer Morhen. If it doesn't, then you don't have many kills left. It's recommended to wait with farming the kills until after the battle.
BiggD
There are a few ways to get this achievement. You can kill an enemy by igniting swamp gas with Igni, shoot a crossbow bolt at an explosive barrel and hope it kills your opponent, or you can even cast Aard on your opponent and then move in for an insta-kill with your sword as they lay on their back. Before attempting any of these methods, just remember that it would be wise to whittle down your opponent's health before using the environmental objects to finish them off. Additionally, this achievement may not necessarily come naturally during your playthrough, but you can always return to areas where environmental objects/effects appear frequently, such as the Crookback Bog swamp.
NOTE: Several community members, including myself, have ran into a beneficial glitch for this achievement. When fast traveling to the Harpy Feeding Grounds in northwest Velen, some Harpies will randomly die mid-flight and fall out of the sky. Even though only 2-5 Harpies will submit to this "random death," the achievement will unlock. Try this method out soon in case it gets patched!
Skorgron
stratege.ru
stratege.ru
Beehives with Aard bees. Dropping an enemy ledge with an Aard also counts.
If you see barrels or beehives, do not be sure to immediately use them, lower the enemy’s health by at least half and then lead him to the “traps”.
dark_lurker799
stratege.ru
stratege.ru