This is a VERY easy achievement to earn! You just need to play any mission on HARD or higher and get downed by a Cloaker.

This is best done in multiplayer. Pick a mission on OVERKILL difficulty and have your ally protect you from incoming cops while you hug a bulldozer and rapidly circle around him in one direction to avoid getting shot. You may wish to fire a few rounds into him or toss a couple grenades at him to soften him up. Repeatedly knife him until he falls. (Remember: You only have to use the knife to get the killing blow - you can do whatever you like to weaken him.)

If you're doing this alone, you may wish to bring AI to protect you from surrounding cops while you do in the bulldozer. However, the AI may attempt to shoot the bulldozer, so your kill may be stolen at the last second if you're unlucky.

It helps to be specced for pistol damage within the mastermind tree. Mod a deagle pistol for maximum damage if you can and then head to any HARD or higher difficulty mission. Then, look for a Cloaker, but do not get too close to him or else he'll simply roundhouse kick you. Instead, keep within average distance of him so you can trigger his charge and his goggles start glowing and making a noise. Once he begins to charge, unload your pistol into his head as quickly as you can click and you should be able to obtain the achievement.

Pick your favorite knife and a HARD or higher mission with a lot of obstacles. Generally, you want to choose an area with a lot of tall obstacles like counters, shelves, trees, mail boxes, door ways, etc.
One such area is the Twenty Four Seven store which contains many shelves for you to circle around.

Charge up your knife, peek around the corner of whatever obstacle you chose, poke the cloaker, and then quickly retreat. Keep the obstacle close to you and crouch so that he doesn't jump over it and into your face. Try not to expose yourself for too long either or else he'll charge at you.

An easier method is to have the AI or a friend distract the Cloaker. While the Cloaker is busy beating the living daylights out of whoever you bring, fully charge your knife and carve him a new one. You may wish to soften him up a bit before you do so because the moment you go in, it's likely that the Cloaker will turn his attention to you - make that knife attack a strong one so he can't retaliate!

Simply equip the fists, charge up, and punch law enforcers around corners and door ways to prevent yourself from getting killed in the process. Play on NORMAL difficulty unless you think you have something to prove.

Simply pick a mission and set it to OVERKILL difficulty so that you get a large number of law enforcers after you. After a bunch of them show up, get up close and aim for their heads. Use the KSP if you're having trouble with ammunition - it has high capacity.

Bring ammo bags with you along with your favorite machine gun to any mission and set it to any difficulty (higher difficulties may result in faster completion). Then, just hold out and squeeze the trigger until you get the achievement. If it gets rough, find a tighter area with a single entry point such as the security room in Framing Frame day 1. Otherwise, enjoy the carnage.

It helps to be specced for shotgun damage within the enforcer tree. Pick your favorite shotgun and head to any mission on HARD or higher difficulty. If you have a friend, have them bait the Cloaker's jump and fire away when they use it. If you're alone, use the AI to bait the Cloaker and fire away when they jump. You may also attempt to trigger the jump yourself by running up to a Cloaker and getting his attention, but make sure you're ready to fire - they move quickly.

Reduce your HP to 25% using whatever method you wish and then proceed to knife FBI units (the ones in heavy tan armor/green outfits). The mission must be on OVERKILL difficulty, so I suggest you pick an area with a lot of obstacles to prevent yourself from getting shot up. It helps to have the enforcer's iron man skill aced for those shield units as well, but it isn't absolutely required. Other than that, it shouldn't take much effort to stab a cop to death. Try to get the jump on them or else they'll quickly counterattack and knock you a mile back.

This particular achievement requires quite a bit of time, so make sure you're prepared before you begin. Multiplayer is recommended so that you have extra hands to move the engines and more supplies such as ammo bags or medical bags to use. Start up a Big Oil mission on OVERKILL difficulty and proceed through day 1 normally. You may wish to secure the additional items on day 1 through stealth, but it isn't required.

On day 2, it's highly recommended that you successfully stealth the beginning portion of the mission. This will make it a lot easier for you to transport all of the faulty engines and the correct one because you won't have the cops shooting at you while you're snailing to the landing strip.

Peruse this guide for assistance in determining the correct/faulty engines: http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=171592213
Once you have your faulty engines and the correct engine picked up, keep them in two separate piles somewhere near the landing strip. One decent location is behind the tree on the far side of the map next to the landing strip. Another location is the little pit behind a log along the same wall. Honestly, the location doesn't matter too much as long as you're both near the helicopter landing point and you have plenty of cover. From there, drop your supplies in a safe location and hold out until you toss all of the engines into the helicopter. Make sure you toss all of the faulty ones in first - keep those two piles separate in order to differentiate between them! If you accidentally toss in the correct one before all the faulty ones, you'll have wasted all that time.



Side note: Some people have mentioned that camping in the engine room works. Try that method if you're having issues with the achievement. Basically, when the helicopter pilot says he'll be there in one minute, grab an engine and run it down to the helicopter landing point while everyone else is protecting you. Then, run back to the engine room after you've tossed it in and repeat.