Gotham City Impostors

The description for this Achievement is pretty straight forward become a nemesis 50 times. To become a nemesis you have to kill another player 5 times in a match without them killing you. You can track your progress in the menus under Track Record>Feats of Prowess>Lifetime>Nemesis Awards Earned.

Here is a strategy if you are having trouble.
Make one of your custom load-outs with the following

Body Type - Mighty
Weapon - Jackhammer/Either Shotgun
Mod - Penetrator ammo (Helps with other Mightys wearing armor)
Secondary - Gatekeeper
Mod - Either sight (in-case you get into a gun fight at a distance gives you a ranged accurate weapon)
Gadget - Glider
Support - Armor
Fun Fact 1 - Horse Healthy (adds health)
Fun Fact 2 - Kinda Bulletproof (decreases bullet damage)

Now as this character use the air vents to fly around the map and use dive-bomb by holding the right trigger while flying. You have a good chance of killing your opponent with the dive-bomb but if you don't you have either a huge machine gun or shotgun to finish them off. Knifing your opponent will also work most of the time.
*With this strategy watch out for airspace deniers (for obvious reasons) and players wielding hatchets (one shot kill on anyone no matter perks, armor, or body type) being so big you are an easy target for this.

Another strategy a friend of mine Sawman and I have been using recently is to take turns being a medic for the other. Using the same load-out above but your friend has a motivator and the care-package. On a map like amusement mile go to one of the choke-points, have your friend throw down a care-package and then use the motivator while you and the rest of your team mop up. If you can choose a choke-point next to a heal point already on the map you are practically indestructible.

*sirbradenwalker had a great idea, having a friend use the targeting goggles the entire match. That way you would be able to find the same character over and over and pick on them. sirbradenwalker managed to get 3 nemesis awards in the first match he tried it. Thanks for the suggestion! If anyone else has good strategies please let me know and I will add them to the solution.

*PointySpred gave the load-out below which includes some DLC weapons that didn't exist when i wrote the initial solution.
I found a slightly different load-out that worked a lot better for me, plus I was able to do the weapon challenges with this strategy.
Body type: Burly
Weapon: Falcon blade
Secondary: Gatekeeper
Mod: Penetrator ammo
Gadget: Roller skates
Support: Armor
Fun Fact 1: Horse healthy
Fun Fact 2: Kinda bulletproof
Rampage: Eagle eye

With my " Burly Ninja" ( I used all my coins to get the ninja and samurai costumes completed). LT is your best friend. You can take a full clip easily while blocking and when they reload you move in for the kill, its too easy. Hilarious to do circles around a health station and watch someone run completely out of ammo then try to run away. When you see everyone at a choke point, immediately take the long way around and flank, use falcon to mop up everyone not watching their six! You don't show on radar. Running around with your blade I'd say about 60% of the time a teammate would start to follow with a motivator, making you unstoppable. Doing this will get the falcon challenges done too. Make each swipe count, don't run in slashing away, keep moving, use the skate ramps for quick escape, learn the maps and choke points. Plus its bad ass when you unlock the gold paint for your blade.

You become someone's nemesis when you kill him 5 times in a match without him killing you.
As a nemesis, you'll earn 100 extra points each time you kill this opponent ( it lasts until he kills you or become someone's else Nemesis).

You can keep track of your progress in Track Record > Feats of Prowess > Lifetime > Nemesis Awards Earned.
You need to reach level 4 in that category to get the achievement.

Edit : Thanks z 4assed monkey for the english version of the path to track progress.

One of the above solutions mentions having a friend use the targeting goggles. I found this much easier using the goggles myself. The goggles allow you to locate anyone on the map. If you are the one using them, you can track your targets movement without actually tagging them. This is beneficial in some cases as it makes it harder for the rest of your team to kill your target before you get to him or her. When you've chosen your victim, try and ignore everyone else and head straight for your target. Since you can track his or her movement, try your best to come from behind whenever possible. Once you get the hang of it, you can start choosing two targets per round.


When choosing a target, look for players with stand-out features that are easy to track. Possible features include:

Body type (example: If there is only one mighty)

Gender (Since there are more male than female characters, there's a good chance there will be only one or two females.)

Mascots (Keep in mind that mascots usually signify a skilled player)

Unique Cowell/Hair (Example: The Mohawk Joker hairstyle is easy to track)

Unique Cape (Players with large capes sometimes stand out)

Weapon (It is easy to distinguish players using a sword or bow as a primary weapon)

ALWAYS WATCH FOR IDLE PLAYERS. Players who are inactive are easy kills and since you have the goggles, you should be able to hunt them down before the rest of your team finds him. Keep in mind that these players will time out, so you have to be quick. Using the tracking method I was generally able to get at least one nemesis on most rounds. Occasionally I got two and sometimes none at all. If you don't see anyone that round with stand-out features, go for any player with the default set-up (tough with no customizations). This is sometimes a good indication of an unskilled player. If there is just not enough character diversity, you're going to have to just play it through and try again next round. I played on Team Deathmatch as it lasts longer then any other mode.

Boosting Method: There are 2 ways in which you can boost this achievement on this game, but the organisation for both methods is the same.

Organisation

In order for you to boost this achievement you will need to have at least 12 people including yourself which can help you. This will prevent randoms from joining your lobby. It is advised you create or look for boosting sessions to help you. A match can be started with 6 people in total, but the risk of randoms joining the match will be slightly high.

If you are the host for the session you will need to organise the parties in a way which suits you the best. I personally put the group in 2 different parties with 6 people each. At the same time you will need to find 2 people (or 1) that are willing to host an in-game party. It is suggested to have one of them in a different party than yourself.

Once you have the 12 people arranged, the people who are hosting an in-game party need to press the in the Main Menu of the game and then press to Start a Private Party. They can then invite everyone in the party by pressing or using the guide and then going into the XBox Party. If all 6 people are connected to each other it means they can play along. If however someone cannot connect to your party, that player may need to restart the game, XBox or router or worst case scenario, swap teams.

When everyone is in position and ready, the 2 party leaders need to communicate with each other and get ready to search for a Psych Warfare game. Since they are the host, they will take the remaining people with them wherever they go. Once they have searched and found each other, the 12 people should lock the lobby and prevent randoms from joining.

Boosting Method 1 - Credit goes to Paul Zap: When the match begins the boosting method is to have one player from each party to send a Chat Invite to another player on the opposite team.

It is highly recommended the host of the session gets a piece of paper and messages everyone on Trueachievements and XBox (Message) assigning them a partner for the session, unless they have friends they rather partner with.

When the 2 players are in a chat, you both need to decide a location where you can easily meet up. Once you have both found each other, you will need to decide who is going first for the Nemesis. Once decided the person needs to simply kill their partner 5 times in a row without dying earning them a Nemesis. Once that's done the other player then claims 5 kills in a row to earn a Nemesis as well. Rinse and repeat this method throughout the match and the remaining matches until you both get the achievement. If one of you gets the achievement, notify your partner so that instead of getting 5 kills in a row, you can only get 1 kill to speed up your partner in getting more Nemesis.

If you both get the achievement, a recommendation is to take turns getting a certain amount of kills which will progress towards your rankings and other achievements.

Boosting Method 2 - Credit goes to the Late Handydarkness. RIP My Old Friend: When the match begins, both teams need to meet up somewhere on the map. The party leader needs to then choose a player who is going for the kills first. Once decided that chosen player needs to put themselves in a corner away from everyone else.
Communication might be needed between the 2 parties to prevent confusion.
When the players are in position, the players on the opposite team that are getting killed need to line up in front of the player who is taking the kills. Try and have both the killing players on opposite sides so that everyone can easily figure out where there going. Then when everyone's ready, the killer can claim kills on 5 people at once. Rinse and repeat this method until they get 5 kills on the same person. This should equal around 25 Kills giving the killer 4 Nemesis at once. Once that's done get the next player going for the achievement to swap positions with the killer and let them take kills.
Rinse and repeat for everyone else. If someone gets the achievement during this method, they need to notify the leader so that they can be removed from the killing spot in the team, speeding up everyone else process in getting the achievement.

Disconnections

Sometimes when you start a new match or you play on a certain map, you or one of the other players on your team may get disconnected from the game, XBox Live or even automatically placed on the XBox Dashboard. If the player has been disconnected to the main menu then you can re-invite them by using the . You'll have to do this quick though before randoms join. Having said that though, if you are not the host of the party the game will attempt to re-connect you with your team. This cannot be done if you are disconnected off XBox Live or on the Dashboard.
If all else fails and a random player manages to join your match then the recommendation is to finish the match as quickly as possible and then get the host to return to the main menu. By doing this they will take all the players that are in the same team as them and then they can re-invite anyone into their game party that's missing.

Note: If you are the host and you get disconnected from the match and returned to the main menu then your team will get disconnected and returned to the main menu as well. They will however remain in your in game party. If however you are disconnected from XBox Live or returned to the XBox Dashboard then your party will be removed from the match and will be returned to the main menu of the game, without being partnered up with anyone else.

Tip: Unless you are going for the "Total Victory" achievement, I recommend you Veto and skip the Docks map. This can be done by pressing on the lobby menu. This is an extremely glitchy map and it's guaranteed a team or a player will suffer connection issues with the game.

Other Achievements

Now whilst you are doing both methods it is possible for you to get this achievement if it's requested with the leader or your boosting partner...



You will be getting kills with Weapons in the game, so you can also work on this achievement...



You can also work on a Gadget or Support Item which will progress towards this achievement...



And you can also attempt to win on the map you are playing and progress on the Slap Happy Kills which will progress towards these achievements...





Good Luck!