Lost Planet 2

First let me say that if you are trying to complete this game this should be one of the the last achievements that you should go for. First get your noms, good jobs, and other online achievements done so that when you come to do this you only have to do a few hundred matches instead of 500.

GUIDE:
Go to player match and create a match with these settings-
Game Type: Team Elimination
Team Elimination: VS Annihilator
Players: (How may people you are playing with, the number of people doesn't matter as long as there is at least 2 people)
Private slots: (Number of players excluding you)
Map: Pirate Fortress
Layout:3
Team Change: ON

DIRECTIONS:
As soon as the match starts have the blue VS leader jump off the cliff and once that is done you get one match in about 45-60 seconds(that is with the loading times).To speed things up have the suicide VS press in the left stick while moving left or right when the match begins, this will result in a short burst that propells you sideways faster. You can switch around which person will be doing the jumping off so that you can take a rest and watch some TV or do something else, to do this simply change teams so that it fits your needs. If you are doing this with only one other person I would suggest you switch host every once and awhile because there are two Noms having to do with hosting and they are-
The Challenger - Play 100 Matchs as a Guest in someone's game.
Emcee - Play 100 match's as the host.

A second solution to Dropshots goes as follows:

Elimination
Yourself, and either a dummy account or one other person
Type: Fugitive
Map: Dual Complex

Dual Complex is actually a better map for suiciding then Pirate Fortress. Its literally a metal cat walk surrounded by death giving waters.

-Basically only one account needs to do anything, so either a dummy account is fine, or your partner literally can just turn on the xbox and walk away

- You must chose to be the fugitive at the start of every match, hit rb its in the menu

- Then simply run off the side of the platform, its takes 4 suicides, but it literally takes under a minute to finish each match; the beauty of dual complex is that no matter where they spawn you, you are basically a jump away from being able to suicide versus pirate fortress which only has the crease at the top

- as long as you hit rematch, the other player never has to do anything, and simply chose to be the fugitive and start the next match

- Just some simple math to give you an idea of time it will require; you need a 100 wins, so the assumption is when you start boosting for this with a 100 online wins; so assuming the high end of the spectrum a minute per match - 400 matches / 60 minutes = 6 hours and 40 minutes total

On the short end of the spectrum - 27 seconds for respawn + 5 secs per suicide = 42 seconds per match; translates roughly to 4 hours and 40 minutes

So it will take somewhere between 5-7 hours to get 400 wins.

Important: DNF is in play in player matches as well, so make sure not to leave any matches early or if you do, make sure to play enough matches to get it back to 0 before attempting ranked matches to finish or start the gunner achievement

Edit 2: using shots setup switch the area to dual complex vs annihilator, match time is between 20-30 seconds , although with in between load time and setup, you will probably be closer to a minute if you are going in rapid succession

Edit 3: Just an update, achievement unlocked today after 3 or 4 games. So I played a total of about 6 hours strictly for this achievement.