Darksiders Genesis

There are 7 snakes on the 7th mission "Decay". Check out the video below to see the location of the snakes. One important thing to note is that if you fight or shoot around the snakes they will begin to flee. If they escape before you kill them then you will need to restart the level.

You can start the level, speed run to the snakes and kill all 7 in 2-3 minutes.

Credit to Wise Guides for the video.

This comes straight from the steam walkthrough wich can be found here.
https://steamcommunity.com/sharedfiles/filedetails/?id=19665...
Credits to Omega Ridley

Defeat every snake in Decay.

Notes: There are seven snakes in total in Chapter 7, Decay. The best strategy is to shoot them from afar, as they’ll flee and then burrow into the ground if you approach them. If they manage to get away, you’ll have to restart the level as the achievement will become impossible to complete.

The first two are near the start of the level. As you enter the large swamp area, you’ll be ambushed by a group of demons. Defeat them and head east, drop into the water, and look for a chest to the southeast. The first snake is next to it. The second one is found about twenty meters north of the first, under the wooden bridge.
The third and fourth ones are located near the entrance to the tomb of the warrior. As you make your way up the steps past the horse-blocking seal, look west down the hallway carefully, and you’ll spot the two snakes running away. Use Strife to take them out before they vanish.
The last three are found as a group behind a secret waterfall to the southwest of the steps leading to the tomb of the warrior. You’ll have to grapple across a chasm to reach the platform, where you’ll get attacked by a couple of demons. To the left are some stalagmites, and behind them, almost invisible, is the hidden entrance to the cave where the last three snakes are found. Take them out to unlock the achievement !

And in case all of this wasn’t enough, I’ve prepared a map for you to use as a reference:

In this video guide I will show you how to defeat every snake in Decay. So to start off there is 7 snakes in total. They are located in three different areas. An important note to take is that if you fail to kill them quickly, they will leave the map. Then you will need to restart the mission over.

First area is right next to where you start, also right by the trickster door. Just head to the right side of the map into the swamp area. When you go into the swamp area there will be one on the bottom part of the loop, and one on the top. If you are riding on the horse, make sure to use Strife. While riding as Strife you can aim his guns to see the snakes when you get close.

The second spot is further up north by some stairs. There will be a conversation at the bottom of the stairs for further reference. Head to the top and continue straight down that hallway. A little over halfway there will be two snakes side by side in the hallway.

For the third spot. You will need to head back downstairs and continue on with the map. There is only one way to go really. So follow the map for a bit. You will eventually notice a boss room. Go past it and head down south a bit. You should see a waterfall on the left side. Walk through it and find the last three snakes. Once all 7 are dead the achievement will pop.