Gears of War 3

Here is the easiest way to earn this - me and a friend just earnt this each in a total of 10 mins.

To get this to work you need a friend, and you both need a 2nd controller.

Both players sign a guest in - it must be a guest, not an offline profile (so press Y to sign a guest in, and choose the 'guest' profile from your profiles list).

Player A hosts a Campaign Arcade, select Act 2, Casual.
Player A invites Player B - this will add both Player B and his guest.

Once the game starts - Player B presses 'RT' to take control of his main account - doing this locks him in as Player 3 - the Mauler.
Player A is the host, so he is RAAM, and his guest is Player 2 who is the Elite Theron.

Once you emerge from the E-Hole, start reflecting the COG bullets by holding LT and aiming it like you would a gun.
You will unlock it once you have started planting for the first seeder, as there will be about 12 COGs for you to use. If you down them - do not worry! They either stand-up for you to try again or they bleed-out and it counts.

Once Player B unlocks it, quit out and Player B invites the party to his session.

Repeat the process above for Player A to earn it. Takes under 10mins and works perfectly!

This is quite a simple Achievement to get, the only problem is that it requires you to be the Third or Fourth in a online/local match

The Host is going to be RAAM so he/she will be able to obliterate anything in sight with his/her Kryll Grenades, Kryll Finger, and Big Shiny Knife.

An easy way to get this achievement is to let the Troika bullets bounce off your shield into wandering COG Soldiers.

The only Problem you'll have is if A) You are playing with Trigger Finger friends who need to kill everything in sight; or B) Have poor communication between players.

If Problem A and B Occur (Which they tend to do) You can just reload Chapter 2 and finish off all of the ones you didn't miss.

The Best thing is that it's cumulative and not in one run. So Be Patient, Take your time, and best of luck to ya

EDIT: I Would like to thank Unfcnbleevibl for Clarifiying an error i had made; "From what I can tell as i've tried this multiple times with 2 people. The host (or Player 1 if Local) will always be Raam. The 2nd player to join the host's match will always be the Theron Elite. You have to be the 3rd player or 4th player to get the Mauler. And since this game doesn't allow 4 player local co-op this will have to be done online. If you only have 2 people (at the time, like I did), I suggest having the host log in a guest or 2nd account so that it's the Theron. So that when you join, you're Player 3 and get the Mauler."

Something I believe of note is that it is far easier and quicker to do it on Cog who are weilding Gnashers

Most of the time the bullets you reflect will be from the Cog who you're aiming the bullets at so he'll get stunned, however if you move very close to one weilding a Gnasher, He'll just gib himself giving you an easy 15g

Also try and play with your friends when you try for this since most random people will try to kill them or kill them before you have a chance, and you can also restart the chapter if you need to

Downvotes please state why, thanks

ok guys if your are playing this on 4 player arcade then this is how i fiqured it out, it doesnt matter where you joined the game as long as you are not the host. For you to be a mauler it works on arcade points you have to have the least kills for you to beome player 3 or 4 which are maulers

so yeah turns out after trying a lot of things the host will always be ramm but for some reason when trying it with 3 or 4 players and i did this with both my xbox one and xbox 360 and or had my second account when playing with 3 or 4 players other then the host always being ramm everyone else will be random as the torque bow guy was at one point during all my restarts and testing was player 2 3 and 4 so that showed me that with 3 or 4 its kinda random but not for the host as he is always ramm