• Eat slowly and wisely, your food is your cover.
  
• Plan in advance, you have all the time you need before rolling out of the tube and you can always use the pause menu to figure stuff out.
  
• Sensor bombs are slow, sentries are not. Run if you encounter the latter.
  
• Ennemies' paths are random and you cannot see their field of vision. Do not avoid the sentries, avoid the room they're in.
  
• Desks cover you less than file cabinets though you can (and will have to) crouch behind smaller objects.
  
• Game does not get easier but more complex over time (and experience). Sometimes it will help you, sometimes not.
  
• Tagging ennemies (a clearing condition for the last buildings) is not a science. You can get some by hiding and waiting for sentries to come close (or let them wander to get lasers and walls peacefully) ; you can go berserk ; you might have to do both.
  
• Don't take it personally, some levels come out as impossible (or crazy hard). If you feel you cannot win, you are probably right: forfeit (you'll still get the XP)

Get a feel for Campaign mode.


You will just have to reach the fourth building. Starting from scratch it's pretty easy since the game won't throw too much at you.

Get really good at Campaign mode.


Reach the sixth building. You'll likely be able to accomplish that feat from level 10 onwards but if you're unlucky it might take more time. Anyway, it is as much straightforward as it gets.

Find out how to turn the tables.


You cannot destroy sentries. Period. Yet, there is a way to have them blown to bits. Choose an early stage (building two for instance) and be ready to leave (but don't). Get the attention of a sentry (that should not be that hard) and draw it near the exit tube. At the last moment, leave and satisfyingly watch the lid crush your archnemesis.

Get the most out of your Sprint.


Using Sprint or Sprint+, gather enough food (usually to 100%) to re-use this item before the timer runs out. Given a well-furnished room, It's pretty easy. You can "cheat" this one by using the custom room generator (high percentage of furniture with few walls and the needed Sprint item) but you will need to reach level 21 in order to do so. At this point, coming upon a suitable room is possible just by doing the campaign.

Put on so many jackets that you can't put your arms down.


Just do the 9th challenge (The Juggernaut) and get at least three armors in your five slots. You have other options (custom room) but it's by far the easiest method. For future reference, some challenges/operations are unlocked at the start, other in the campaign mode or by getting achievements.

Learn to appreciate your Dig.


In any level, dig seven or more times. It requires a lot of food but if you get two Digs in a large stuffed room, it should be OK. Dig+ really helps later on. You can also build a custom room with infinite charge, Dig and quite a lot of walls but it can easily be done before having access to the custom menu.

No, seriously. It's a secret.


Use the Konami code[en.wikipedia.org] in the Operations menu (thanks Chichi for the confirmation). For some people (maybe following an update), the escape key may need to be pressed after the code for the achievement to unlock. If you have trouble inputing it (I used a X360 controller), go there.

Max Food/No Damage, four levels in a row.


What it says on the tin. This relies on luck and skill but if you are above level 15, the first two buildings on the lowest difficulty setting should be manageable.

Complete the three Laser-based Challenges.


Complete the laser-porn challenges named "Catherine", "Zeta" and "Jones". Good luck for "Jones" but it shouldn't be so intimidating once you get the feel for it. By the way, it's an Entrapment[www.imdb.com] reference :



Find out what makes a Floor Trap extra angry.


Getting the achievement is fairly easy. Getting there, less so. By reaching level 12 or so, you'll unlock sensor bombs. If you make them explode on a regular heating floor trap, you'll get a super deadly floor trap... and the achievement. There are two ways to make it happen:

• YOLO: get hit by a sensor bomb while standing on a floor trap
  
• Drop a stun trap (you'll have unlocked it by then) on a floor trap and draw a sensor bomb on it

Get two bonuses with a single Stun trap.


The easiest way to do this is in the 4th operation where there are sensor bombs aplenty. Just reload until you find a building where there is a stun trap in the first room (it will be easier) and clear it. Then draw two sensor bombs in a large room, drop a stun at equal distance of them, draw them in and the blast range should take care nicely of things.

A custom room (just you, stun traps and sensor bombs) works too if you can afford it.

And not just the fact that you can teleport in this game. It's a video game. Of course you can teleport.

You can do this as soon as you get the Teleport upgrade (which is in the very late game). Using it will stop the time and you will be able to move freely ; using the item again will restore the situation. The trick is to get in a level where you have to tag ennemies, get the Tagger and just tag an ennemy while in suspended state. This one can be easily done with the next achievement.

It's a certain setting in Custom Level mode.


After level 21, you gain the ability to generate rooms by fiddling with quite a few parameters. You'll just have to build a custom room with no walls (set it to 0) to get this achievement. You will not even have to clear the room. Since it's very easy and boring just to do that, let's try to get the previous achievement (the power of teleportation) while at it.

Build a room whose objective is "Tag", with a Teleport+ item, the ennemies you want and no walls. And have fun.

Become a ninja of Campaign mode.


Finish the game in any difficulty mode. Yes, that's one of the hardest achievement. Upon reaching building 7 (the hard part), you will have a boss fight. Good news: that's the lesser hard part (at least in the lowest difficulty setting). Bad news: if you fail, you'll have to start all over again. Plus the boss can insta-kill you. And you have no armor or freebies or teleport or invisibility. Now you know. So keep calm and be prepared:

• Step 1: Wait until a blue box (Stun) appears and get it. Try not to eat. Evade the lasers, the death from above (a.k.a. the circle of doom) and whatnot. Drop a stun in the path of the boss while it is trying to suck you in. Get rid of the stun.
  
• Step 2: The boss will then try to run you over. Wait for the second blue box (Block) and get it without taking too much risks or too much time. Stay as far as possible from the boss and when it is coming at you, drop a block to protect you and damage it. Get rid of the block.
  
• Step 3: The boss will rotate in the same spot unleashing a ray of death from four directions (as I witnessed it at the very least). Don't be caught in it. Sensor bombs will appear. Get the stun as soon as possible and drop one very close to the boss (you can hide between it and a wall if you're able to). Draw a sensor bomb on it. You can now relax.
  
• Step 4: Enter the boss (I know) and drop a stun. Enjoy the ending.

Show that you're a Campaign pro while starting on a high enough difficulty setting.


Finish the game in one of those difficulty settings. If you are insane. There is no way to make it easier. Sorry.

Here's to helping you relax:

Source[modddy.tumblr.com]

This game has a lot a secrets this guide did not cover (audio logs, secret audio logs, challenges, hidden challenges...)

Have fun finding some of them.