Syndicate

These are my notes from beating most of the levels solo on expert. More than anything it just takes patience, methodically killing everything before advancing. I was able to do 7 solo and 2 with a 2nd xbox that just sat there. Either of those could be doable solo with better tactics or more skill.

Apps
C2C Pulse is a must have, fully upgraded. It will heal you enough to soak the damage from 3 agents long enough to do a chiprip on their friend. (Although you may need a little help from DART mode's enhanced damage protection). It will let you go toe to toe with armored enemies, or stay out of cover rapidly downing grunts and sergeants without having to worry about your survival.
Beyond that, I did many levels with backfire, which does a bit of damage, but also knocks your target down and lets you shoot them for a bit or escape, your choice.
Later on, I switched over to virus, it will do a decent amount of damage to agents, or armors (even before you breach them).
You could also go with battery, so you can use C2C Pulse more often, or reboot, as a get out of jail free card.

Weapons
Kusanagi sniper rifle is an absolute must have, fully upgraded. Abusing it's ability to shoot through walls is the only thing that makes some parts possible.
My usual backup weapon was the CQC shotgun. A full clip will do serious damage to agents or armor quickly, and you don't have a lot of time, so that's good. It's also availale on almost every mission.
Honorable mention to the E-Mace. It's crowd control ability is incredibly handy when you need to protect a dropship or UGV. If you time it right and they are spaced right, you can easily keep 4 guys stunlocked. Not that great against agents or armor though.
Honorable mention #2 to the Riotlance. Not quite as good for crowd control as the E-Mace... but it's secondary fire lets you drop your entire clip at once as some sort of energy grenade. It has a decent area of effect and high damage, it can take down entire groups of agents in the right circumstances.

Dealing with armored enemies
They will hurt you, and you can't kill them that quickly since they need to be breached first. 90% of the time you want to get close enough to start a breach, initiate the breach, then run like hell while it finishes. Ideally, up or down a set of stairs. If you are far enough away from them they won't follow you up or down but will wander around stupidly while you shoot them through the walls with your sniper rifle.
They will only stay vulnerable for a little while and then need to be breached again, until you get their health bar to under 50%.
Reactives: two health bars, then the third breach will kill them instantly once completed. They are armed with minigun or flamethrower. Quite slow to move and to turn. The flamethrower ones are deadlier at close range, so your best bet is to reserve a bit of DART for protection, and sprint past them as far as you can once they get too close (breaching as you run if necessary) and then turn around and shoot them a few times.
Electrics: two health bars, armed with a shotgun. Quite a bit faster than the reactives. Try to stay on a different floor if possible so they are confused by pathing. Otherwise breach and use DART mode to tank them for as long as you can before hitting C2C Pulse. It should last long enough to finish their first bar of health, re-breach, and down them again, with maybe a little more DART at the end if your pulse ends too soon.
Liquids: the easiest of the bunch, one health bar and a shotgun. Basically a weaker version of the electric armor.

DART
The DART overlay is important for two things, shooting through walls, and the defense bonus. There is a damage bonus as well, but that isn't nearly as important as the 1st two things. It will regenerate faster when below 50%, so you don't always necessarily want to wait for it to get to 100%.
It will also regenerate a bit as you get points, so if you are able to kill several enemies quickly it will really stretch it out. If you start getting hit and need to run back to cover, hit DART and it will help you make it there in one piece. If you are shooting through the walls, most walls you can only shoot through in dart mode, even if it's transparent and you have your shot lined up properly, it won't work (Riot shield enemies are an exception however).
You will use a lot less DART if you turn it on briefly then off as soon as you take your shots. Turn it on for a split second, aim in the genral area you saw your target, then turn it back on to finishing lining up the shot and taking it.

Melee
It's worth mentioning that once you are fully upgraded, a melee kill will get you 50% of your health back. And of course it won't use any of your ammo. e.g. at the beginning of Argentina, there are many guys in a small area and you need to drop them quickly, so punching in the face is the way to go.

Levels
My experience won't 100% match yours, the spawns are slightly different with each restart, so you may see slightly different areas or positioning. I'm also not going through every location in exhaustive detail, much of the levels consists of: move out of cover, see guys, run back to cover, shoot guys through the walls, repeat.

Western Europe
You will probably need c2c pulse at the very beginning of the level, as there will be a lot of grunts coming at you at once. Once you've thinned out the 1st rush, you can camp out behind the hut or near the start area and pick them off through the walls.
After getting through the gate, once the liquid spawns, hit c2c, run up and start breaching as you run back into cover. then get him down to tramua status by shooting through the wall then finish him off at your leisure.
On the boss, run up to get a luck then drop his armor while running. get him down to vulnerable and finish off first armnor layer asap. then if he comes at you, you can finish off 2nd layer using c2c heal

Mozambique
After returning the first 4 hard drives there will be guys, lots of guys, perhaps all of the guys, up on the rooftops shooting at you and your dropship, but they will end, eventually. No one else will hurt your ride after this fight so it's okay if its health gets low.
They will also include a liquid and reactive at the beginning and another pair later on. At the very beginning of the checkpoint, I sprinted across and up the stairs and picked off the reactive by shooting through the floor of the helipad (run out from under it to get your lock).
The liquid has a rocket launcher and won't use it at close range so is easy enough to finish off if you pop C2C to keep the grunts from killing you while you focus on him.
Once they were dealt with I sprinted back to the security room by the dropship and peeked out and slowly killed them off. The 2nd reactive seems prone to getting stuck on the roof right across from the dropship and will just sit there while you shoot him.
If he doesn't and gets too close, breach while you run back to the lower level on the other side, or down by the level start and abuse him with your sniper rifle.
While getting the 2nd set of hard drives you will face a flame reactive. Do not get close, breach and run, continuing to retreat back outside (all the way to the ship if need be) as you shoot him through walls and from beyond his range.

Atlantic Accelerator
1: The room with ammo near the start point is a good place to camp out. The reactive will eventually come over, but there is enough cover that you should be able to run out and drop his armor and finish off his first life bar before he gets to your hidey hole. Then if he gets too close, use C2C and tank him.
2: There is usually a liquid in the next section, but he is not a big problem, feel free to use C2C to make it easier.
3: nothing special here usually
4: nothing to see here either
5: At the final checkpoint, hide under where you entered behind hte pillars near the ammo. Usually one agent will rush you. You may have to retry a few times until it is escobar, the healer. He really needs to be killed first.
Once he is down its easy. Backfire/Virus him and hit him with your shotgun. Use c2c when you need to and to stay alive as you chiprip him.
If ochoa (minigun) is the 1st one to come you will likely die, he is too tough to take down while being healed, unless he follows you out of healing range. The other two will go down from a full shotgun clip at close range even if being healed. I would avoid using c2c if you can as you will want it to take out escobar.
Once Escobar is gone, you can down the others repeatedly through walls to recharge your apps. When everything is ready to go, weaken one to near death, pop c2c, rush him, and finish him with the shotgun and chiprip. After each agent dies you will get some normal soldiers/sergeants but they are not a big problem to deal with from your cover spot.
Shoot them through the walls and shotgun any who come close.

Colorado
Fire reactive, right off the bat, woo! Kill the two grunts then run inside and hang a left. Mr. flamey will usually aggro on the dropship, which is unimpressed by his flamethrower (he did zero damage to it).
You can run out, breach his armor, run back and shoot him until he dies, there is ammo in the small room just to the left of the entrance to the building.
As soon as you go through the metal detector, run back out to helipad and make sure to mow down the electron mace guy pronto, followed by his friends.
Head down the stairs to your objective but be ready to run away outside again as soon as you go through the blue light as another strapping young lad with an E Mace will be coming at you with his friends.
As you bring out the first sample be prepared to drop it as soon as you go through the light as there will be a welcoming party on the stairs and you may want to have your hands free to use your guns.
Then when you get out to the pad there will be a whole mess of sergeants and grunts. Head back inside and take them out through the floor as quickly as you can.
There is no one particularly dangerous in this group, just numbers. Do the best you can to protect your dropship (mine was at 85% after this group), while it will go back to full any time you restart, you do need to get to a checkpoint and it is a while yet until the 1st one.
You may want to pop a C2C so you can gun them down quickly and then take cover once it wears out.
Once they stop coming, don't actually put anything in the dropship yet, just dump them on the pad nearby.
After grabbing #3, a reactive armor will be coming down to play so drop the sample immediately in the room where you got it. Try to breach him as he comes downstairs then retreat back to the sample room and hit him enough to make him vulnerable.
Then you can rush past him and back to the helipad and he will stay downstairs so you can shoot him through the walls with ease. He may come upstairs when you go back down to breach him again, but you should have no troublw downing his armor again before he gets too close.
Once you have all 4 on the pad you can turn them in one at a time. After #2 a whole bunch of sergeants and grunts will start shooting down from the balcony in front of your ship.
You may want to use C2C so you can just stay out and tank them and your dropship will take minimal damage (mine took another 2% to 83).
After #4 you will face a liquid armor and a few grunts, plus the turret on the left roof will activate. Pop C2C, start breaching the liquid and go wild with the shotgun on the grunts (and the liquid once his armor is down).
As you go up the stairs to turn off the turret, there will be another liquid so breach his armor, greet him with 12 shotgun shells, and then run away a bit if needed.
There are a couple UAVs and a turret up top so breach/kill the one UAV you can, then sprint into the shack to disable the turret. A whole mess of regular guys will come out of elevators opposite you nicely lined up for your sniper rifle.
Go inside and override security. Congratulations, CHECKPOINT!
Head the back stairs (red rectangle over them), 2 reactive armors will show up (one gatling and one flame), breach one and run away.
Try to kite the flame guy down towards the dropship then sprint away. Hopefully he will sit there uselessly roasting your dropship. Then finish off the gatling one.
A lot of guys will come once the first reactive dies (I think, or it could be time based), lots and lots and lots. They will mostly be on that upper balcony in front of you. Some will come down and come out on the lower level by the metal detector.
The shack that had the turret control is a great camping place. It has ammo, and the guys up top can't hit you, so you can run out, acquire some targets and kill them. They will come slowly for the most part, 2 or 3 at a time. When guys come below, you can pull out your shotgun, hop down, and blow them away before running back up. Have your C2C ready just in case.
Be sure to reload when you have a moment and grab ammo when you can.
Eventually a dropship will come (you'll need to breach its turret to disable it). It will drop off 4 sergeants and 4 grunts on the upper level, be careful though as it may land on YOUR rooftop. After this you are finally done with the waves of enemies and can finish off 2nd reactive armor if he is still around.
You can now head up the stairs to that balcony where all the enemies were showing up, there was a E Mace down the hallway where the reactives started out, one grunt straggler up top, and a UAV.
After you bring back two cases, 2 reactive armors will spawn. You can play cat and mouse with them all over the place, save your C2C if you can in case you get pinned between them. Beware, the bottom room where you got 1st 4 cases has some grunts and an E Mace guy that respawn in it as I learned when I tried to hide there. (There is no need to kill them off, but you may want to, just to give you one more place you can run to.)
Once the reactives are down you can pick up the last two cases and drop them off with no further molestation.

China
I was unable to do the 4th checkpoint solo. It doesn't take a lot, I ended up just using a 2nd account to sit there and make the UGV I was escorting wait while I cleared stuff out.
1: is fairly straighforward, just go slow and steady.
2: at the end of the large street is a reactive armor. Breach, retreat, breach, retreat. You may want to pop a C2C and give him a faceful of shotgun to speed things along. Beware of the riotlance snipers above after you turn the corner as well as they can easily stunlock you.
3: keep your distance as the riotlance soldiers are plentiful and can stunlock you. Save C2C for agent shinobi, and rush him, you need to do quick damage before he heals.
4: this one is a pain. I don't think this is reasonable to do solo. If you have a friend or 2nd xbox, use it to block ugv.
As soon as the UGV opens the wall get in front of it and block it. (you may want to play on normal to get a feel for the patch of the UGV so you know where you need to stand to block it).
Peek around the 1st corner and deal with the liquid armor that comes. You may need to use C2C.
Kill some grunts and sergeants from the doorway, then toss a grenade at the tunnel opening, it should kill the electron mace guy waiting just round the corner to ruin your day.
Swing wide around that corner just in case and take out anyone in that section of corridor. Move slowly up the center to the door on the left, peek out a bit and take out guys one by one, a whole lot will jump down out of the pipes in the distance.
E-Mace guys will come out of the door to the left periodically. If you can take them out quickly do so, if not, hopefully no one else is shooting at you and they will have to stop to reload and you can kill them.
Once the enemies stop spawning, you need to let the UGV move up into the start of the hallway where you have been killing all these guys, as many shield & riotlance will spawn behind you (and a few in front), and they are much easier to control if they are coming through that narrow doorway.
You could also try snatching up an E-Mace from the floor at this point to control them more easily. (I was just using the Sniper/Shotgun combo at this point, but the E-Mace may have been a better choice than the shotgun.
5: you can go back to being solo here. You'll face: 1 agent, 1 reactive, 1 flame reactive. Clear out the top balcony in the station and camp there. They will all stay down below. BTW you cannot shoot through the reddish glass panels in the railings, but you can shoot over them, through the floor, or through the cracks between them. The only dicey bit is running for more ammo back at checkpoint. So you may want to try to reserve your C2C for that purpose, and if possible take at least the agent out beforehand.

Scandinavia
I was unable to do the 3rd checkpoint solo. It doesn't take a lot, I ended up just using a 2nd account to sit there and make the UGV I was escorting wait while I cleared stuff out. I would also start C2C on the dummy before waves where UGV was exposed so he could draw fire longer.
1: A few emace and a liquid. There is plenty of room/cover. The cover on the right side gets you close enough to the dual turrets to breach them. Make sure to grab an E-Mace.
2: Hang back and snipe, be alert to enemies popping out of containers on the left and the diagonal one at the 1st U turn corner.
There are multiple waves of both riotlancers above and riot shields on ground at the 2nd U turn right after that, also the upper level containers here may open up and have grunts.
3: 1st fight is right when the door opens, toss a grenade left, then hose the other guys down with your emace.
2nd fight is as the UGV opens a container after going around the corner. I recommend getting up against the far wall and doing the best you can to take guys down quickly. You could go ahead and use C2C here and be a it more out in the open to draw fire from the UGV, or conserve it for later.
Once this fight ends, block the UGV with the other controller and run ahead a bit. After going under a couple of bridges the next group of enemies will spawn, so run back to safety and pick them off.
Let the UGV move through the controller, just after it turns more guys will spawn on top of the containers in front of the UGV. There are some open containers on the left that are a good place to take cover in to finish them off.
Shortly after passing by a forklift your UGV will start cutting another hole and a whole bunch more guys will appear.
After its done, hold UGV and go ahead and deal with a few guys to right. New checkpoint here btw.
4: UGV will now so final breach. Bunch of guys on balcony and roofs to right, reactive and dropship turret at end. Feel free to fall back as your UGV should have enough health to finish its job.
5: Big warehouse, huge number of guys. Use shelves for cover and keep killing them. Eventually the doors at the end open a reactive comes and the regular guys stop spawning.
6: Agent time. Pick off the regular guys and wait for Shinoda to wander away from his friend so you can shoot him w/o taking fire from all of them. When he is near death, rush, C2C, virus, shotgun, rip. Run back to start room and recover. Down other agents to recharge then go after another one.
2 of them are annoying dodgers, one is not and has a coil laser. I'd save the laser guy for last as he is less annoying, so easier to down for recharges. Dodgers need about a second to recharge between dodges, so shoot once, quickly retarget and shoot a few more times.
In any case, recharge apps then for each: weaken, rush, C2C, virus, shotgun, rip.

Northern Territory
1: Lots of guys and lots of cover. Once you kill them there is an electric and a turret at the end, may need to sprint up then run away to strip armor.
2: Very similar to 1st checkpoint but it has a reactive at the end. After you turn off the turret a flame reactive and many grunts will come out as well.
3: long fight, a couple of electrics. If you take out the couple of guys with rockets at the start no one else really hurts the ship. There will be so many grunts at the end, you can run up and unlock the four doors during lulls in the enemies.
I'm not sure if thats what stopped spawns or they simply ran out. Again like in Colorado, bring the packages back but don't put them in the dropship yet. After bringing back #1, a dropship drops off 4 or 5 grunts and sergeants on the pad opposite your ship.
Drop off the four cases once you have them all and you are done. Some guys will spawn, but the level is over before they can even do anything. If not (on Normal I seemed to have to kill some of them off before it would end, but I may not have turned them in quickly enough), retreat back to the start area of this checkpoint if needed.

Argentina
I'd recommend backfire on this one simple because it will knock the healer agent at the end down long enough for you to kill him right away.
1: Once the UGV gets about halfway through the room, the guys start pouring out. Pop C2C and sprint around meleeing (take out ECM guys pronto). Once C2C runs out, hit DART and keep killing guys. You will need to try to keep to cover a bit more behind the pillars at the sides of the room since you are more vulnerable now. Hopefully it lasted long enough that there aren't many guys left. Try not to enter the next section with it totally drained.
2: 2 flame reactives if you have c2c pop and kill the little guys then run around walls whittling reactives, if not sometimes they spawn at end of the wave of grunts so keep trying. The simplest thing is to keep sprinting past them from one end of the room to the other, shooting at them while they are too far away to hurt you, and sprinting past them with a dash of DART when they get too close.
3: This checkpoint is pretty easy. Stay in cover, kill through walls.
4: 2 electrics and lots of grunts, as you proceed and go up to 2nd and then 3rd level, more guys will come out including a reactive, but they are all pretty easy, just retreat and kill them from long range.
5: Here you will face 2 agents, an electric and a reactive. Take out Lars right at the beginning or you are in for a world of tedium. As soon as you hit the switch, go to the door, pop C2C as it opens, turn on dart, and backfire him.
Then pound him with your shotgun while hes on the ground and quickly chiprip him and run back into the start area. After this it's pretty easy, just pop out and hit the reactive and electric until they are dead then eventually snipe the other agent.
If for some godforsaken reason you don't have your C2C charged at the checkpoint (or if the game glitches on you and it is no longer fully charged after restarting), there are endless grunts you can charge it on.
NB: you can't shoot through the window, but can shoot through the wall around the window, go figure.
Unfortunately by the time you do that, Lars will have left his convenient shootable place and be hopping back and forth like an idiot on the top floor.
You should be able to just barely take out a layer of reactive armor if you backfire him and bumrush him with the shotgun after popping C2C.
For some reason, the electric seemed to keep getting healed by Lars even after I took his armor down once. So once the level of grunts was lower and the electric was off to one side, I went after Lars.
I sprinted upstairs on the side the electric was not on, hit C2C (do right before you attack so it will heal you while you chiprip) and introduced Lars to my shotgun, chipripped and ran. After that the rest is relatively simple.

New England
1: Mostly easy, basic guys who stay at range. As you get close to the objective, a turret will pop out as will 4 or 5 guys including an ECM unit, so be ready to fall back. Once you disable the turret an electric armor and 2 or 3 grunts will come out of the door.
2: Ttake cover along the far right wall and you can snipe these guys with ease, several waves but almost zero risk, make sure you go to the far left edge to make sure there are no guys off to the right.
Once you've killed everyone you can, sprint over to a little cubby next to the stairs and take out anyone that is left. As before, once you disable the turret some guys (including 2 electrics I think) will join you through the door.
You don't even have to fight them really, you can sprint through the door with C2C, but it's probably better to get everything fully charged 1st instead.
3: After opening the door you can mostly camp out right to the left of the ammo boxes, there's a nice nook here. The only guys that seem to get close are basic grunts, everyone else will wander about waiting for you to snipe them through the wall.
After killing many guys, the doors at the top back end of the large room will open and a few more guys and two reactives come out. The reactives don't seem interested in coming downstairs unless you get too close, so they are easy enough to kill.
In the long hallway, as you move down, several waves will come out from the left by some boxes, just back up and deal with them.
4: Dual flame reactives. Good times! Intimidating as these guys may seem, this is actually not too bad once you know how to handle them.
Run out, start dropping the armor, then run back to the closed door past the ammo crate. Shoot the guy who is vulnerable through the wall, but don't get greedy, conserve at least 25% of your DART.
Once they round the corner, turn on your DART, and sprint past. They are slow to turn so you will only get lightly toasted. You can even make it without DART on, usually, but it's not worth the risk.
Once you get to the elevators where they came out, turn around and shoot them some more, you will probably have time to unload one or two clips with the sniper rifle.
When they get close again, hit your DART, sprint left along the wall and hang a right when you get to the plants. Go back into the ammo room. Rinse, repeat, grab ammo when you need it.
When they are both dead the door opposite the ammo room will open and four or five grunts will come out. Not a big problem, but now would be a stupid time to die.
5: Fawkes (the healer) needs to die! Try to conserve your ammo by using melee on grunts/sergeants as much as possible. Once you clear the guys on the upper level you'll be spending most of your time in the "server room" directly under where you start this checkpoint.
If peek out into the room with the agents (left side seems to work better), a single agent will usually come to visit. My strategy relies on it being Fawkes, and it's 50/50 whether it's him or Bulger.
If you take out Fawkes, retreat to the server room. A fair number of grunts and sergeants will keep coming from both sides. Hide in the servers and punch them in their stupid faces.
Once enemies stop coming out of the lower level doors, you need to whittle down the health of all 3 agents by shooting them through the walls. Ideally you should get all 3 so the bar is entirely empty or nearly so.
Some of the agents seem prone to dying (and then being rebooted with full health) if they get too low, I noticed this problem with Mikhailov. You don't want that to happen too many times as getting more ammo will be... interesting... as it is in the room with the agents.
More grunts may come if you take a long time doing this, so be alert for that as well. Once they are all on the verge of death, best case is one decides to come after you.
If they do, whip out the shotgun, pop C2C then kill them (w/Virus if possible). His 2 friends will run over to revive him. Before they can do that ... BAM BAM!
If they don't, pop C2C and run in and gun all three down as quickly as you can, maybe throw in a virus to deal with one as you shoot the other two.
Once all the agents are down, quickly chip rip all 3. This will prevent the annoying reinforcement waves with Liquid/Reactive armors from spawning.
You will just need to clean up the half dozen grunts and sergeants that remain and you are DONE!

Some general guidelines for this achievement (for more details check Palesius solution):

1. It's better to try this once you complete all coop maps on lower difficulties, that way you will get an idea of where to go and what to do in what time. Still, there are some diferences between dificulties. The most important one is the spawning of some type of units, some of them in higher number (e.g. liquid armors) and some of them does only appear on expert (e.g. mercenaries).
2. You will need some very good upgrades and everything fully researched (weapons and apps) in order to endure longer and hit harder. For that you will need to replay coop maps on lower difficulties (this help to get CEO achievement). My weapons sugesstions are the Kusanagi sniper rifle and shotgun. For apps I recomend the C2C Pulse, it is quite a life saver, and the damage amplifier, it helps a lot with heavies.
3. Last but not least important: Try this with a 4 players team and if possible with players you know and you can communicate with. Randoms give up quickly after getting owned by the enemies and, in case they don't get owned, they will go on their own, working only for themselves and letting die their teammates, leading to a mission failure.