During Psych Warfare matches after the other team attach the battry to your teams motivator and the countdown reaches zero, another countdown will begin. During this time you will not be able to shoot, though if you hold the fire trigger you will perform a slapping animation.

Kill the enemies with this slap 50 time and you will gain the achievement. It's very hard as opponents will be able to see you on their radar during this time and their gun fire pushes you back. It is best to ambush enemies as they chase your team mates.

You can also use the panic-slap melee attack at the end of a losing Fumigation match, but the window of time in which it is possible is very small, before you die from the poison/bats.

When you reach level 100 you will be able to accept a promotion, getting to level 100 will take 2,5000,000 EXP so complete as many Feats of Prowess as you can.

Gadgets and support items are unlockable after level 3, but you will not gain the ability to complete the feats related to them until level 15 for Gadgets and level 18 for Support Items.

Each gadget/support item has it's own different feats that need to be completed. There easiest item to complete the feats for is the Motion Sensor support item as you do not have to kill anyone for it's feats; just run around using the Ninja Smoke Bomb gear to stay hidden dropping the motion sensors in high traffic areas or near objectives, every time it recharges drop another one and by the time you've detected enough enemies you will have dropped more than enough to complete both of the items Feats of Prowess.

Kill 10 enemies without dying; your best bet is to do this in an objective game type, hang back and allow others to run forward and soften up enemies as finish them off from range.

Play your first match; Start the game and select play now, then you have the option of either Team Death Match, Fumigation or Psych Warfare; pick either one of them and after the match is over the achievement it yours.

You gain access to the Impostor Customization menu (Secret Identity), your first loadout slot and unlock tokens at level 3, use an unlock token on any loadout item and the achievement is yours.

The ability to unlock costume items isn't available until level 8 after that you can use costume coins to unlock any costume item and gain the achievement that way.

You gain access to the Feats of Prowess of Weapons at level 10.
Particular feats are different for each weapon and the game has several different types of weapons that cater to different play styles. 

Rifles, Submachine Guns, Heavy Weapons and Sniper Rifles are good for people used to playing first person shooters as they usually have: X amount of kill, X amount of headshots and X amount of kills with each mod equipped; as their feats, although the (Heavy Weapon) Deep Freezer is different in that it has feats for inflicting damage with the weapon as well as shattering enemies with your knife after freezing them instead of kills and headshots.

If you have difficulty gaining headshots, you may prefer Shotguns as they need close kills instead; though you have to be more or less right next to the enemy when you gain the kill. Launchers are good for people that prefer ambush attacks and need muti-kills instead of headshots.

If enjoy playing Medic you may find that the Motivator is a good weapon to use for this as it doesn't require any kills (as you can't do damage with it) or mods (there are none), just healing. Although the feat to gain 1200 healing in 10 seconds will take teamwork, as you will more than likely need to heal 3 to 4 players using the Mighty body type while they are under constant fire.

In a game of Fumigation you must gain a second Gasblaster for your team when the enemy team has less than 10% to go until victory.

Play though each of the gamemodes until you have a victory on all of the 5 maps for each gamemode.

When you start the game select play now and then Initiation; complete the brief tutorial to unlock this achievement.

There are 75 Challenges in all but you only need to gain the gold medals for 50, in order to gain the gold learn the course and at higher difficulties the placement of the targets.

For videos of how to gain the gold medals see darkenednight's post here.

To become someone's nemesis you must kill them 5 times without them killing you; it doesn't matter if you die by someone else's hands just as long as the person who you keep killing doesn't get a revenge on you. 
You can view how may times you've become someone's Nemesis in the Lifetime section of the Feats of Prowess menu.

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