Shadow Burglar is a short, free, but great stealth game. The game has 2 levels, the first level, Train Station, only has 1 map, while the 2nd level, Ship, has 2 maps. For convenience, I will refer to the first one as Lower Ship and the second one as Upper Ship. The levels are quite linear, with only a few side rooms, usually containing collectibles.

Important things to know:

• The game has no saves or chapter select, and must be completed in one sitting. You exited the game after finishing Train Station? You'll have to play it again. Checkpoints are still there though, so if you got caught you don't have to replay the whole map.
  
• Achievements may be a bit buggy and not unlocking despite fulfilling the conditions, or vice versa, unlocking even if you don't fulfill the conditions. If it didn't unlock, the only advice I can give is to close and re-open the game.

A Ticket to Nowhere: Awarded for finishing the first level.
Story-related. Should be earned after completing the Train Station level.

All Aboard: Awarded for finishing the second level.
Story-related. Should be earned after completing the Ship maps, and finishing the game.

Pacifist: Awarded for finishing a level without taking down a guard.
Easily done in the first level. When William tells you he can take care of the guard blocking the way, don't do it, and instead wait until his lantern is not shining the path, and in your shadow form, quickly run past him.

Ghost: Awarded for finishing a level undetected.
Easily done in the first level, too. You can kill guards and still get this achievement, don't have to pair it with the "Pacifist" achievement.

In the Shadows We Thrive: Awarded by learning the art of the shadows.
Unlocked by using William's power to eliminate a guard. There's a guard that's not on your path early in the first level, but eliminating him doesn't unlock the achievement for me. Then you'll meet this one directly on your path with a prompt to take him out. When you're close to him in the dark, press F.


In the Shadows We Distract: Awarded by learning the art of distraction.
Unlocked by using a gramophone to distract a guard. There's a prompt to do this near the end of the first level, and it's pretty much the only way to get through.


No Mercy: Awarded for taking down 10 guards in a game session.
Basically, eliminate 10 guards following the same method as "In the Shadows We Thrive". Can be done across multiple maps, doesn't have to be in one level.

There are 4 collectibles in this game, all of them located in the Ship level. 3 of them in the Lower Ship, the last one in the Upper Ship map. They are marked by a lit lamp in their respective rooms. There aren't any in the Train Station level.

I See You: Awarded for finding the glasses collectible.
Early in the Lower Ship map, after exiting the luggage room, you will be in a hallway with stairs. Instead of going up and alerting the guard, go to the barracks room at the left. You will see the glasses on a trunk with a lit lamp.


A Stylish Thief: Awarded for finding the top hat collectible.
Later on you will have to pass a brightly lit hallway, and your only way to cross is by teleporting to the guard's shadows. There will be a wall with 2 teleport points, go there, and you will pass a dining room. The top hat is on a chair, near a lit lamp.


Time is Money: Awarded for finding the pocket watch collectible.
Next you will pass a kinda dark hallway. There's a room to the right, with many barrels and sacks. The pocket watch is located on a trunk with a lit lamp. If Jean says the line in the image below, you went a bit too far, go back to the previous hallway.


Film Noir: Awarded for finding the camera collectible.
The only collectible in the Upper Ship map. From where you start, you will see a lit room across from you, behind a sailor. Enter the room, and the camera is on a table near the fireplace, again with a lit lamp on it.


Collector: Awarded for finding all collectibles.
Will be awarded if you collect all of the collectibles. Not sure if it has to be in one run or not, but no big deal since they are very easy to find. However, it may be buggy, I unlocked it after picking up the pocket watch, before I even reached the Upper Ship.

Konami Code: Awarded for unlocking the secret mode.
Basically enter the Konami code in the main menu. It's a well-known input. If you're on keyboard like me, press up-up-down-down-left-right-left-right-B-A using the arrow keys. Or replace the arrow keys with WASD if it's not working. If you do it right, you will hear a little jingle.

If you're using an Xbox controller, it's still the same keys. However if you use a PlayStation controller, substitute the B-A with O-X, which are in the same spot as the B-A in Xbox controllers.

The achievement may be bugged and not unlock even after pressing the correct button. The solution is to click on the Shadow Burglar logo in the main menu with a mouse, and input using the arrow keys. The sound can be replayed and will still play even after you unlock the achievement.

Using the code unlocks some secrets, aside from the achievement. The secrets are:

• A poorly-drawn Jean in loading screens.
  
• Unlimited sprint stamina.
  
• Ability to jump by pressing the Space button.

The hidden features doesn't enable you to access new areas, get new endings, or anything, but you are able to move faster without worrying about the stamina, and the ability to jump provides a better sense of "movement freedom" while also allows you to skip some parts by jumping over.

Thanks to KiruChan for discovering what the secret achievement is. Here's the guide they made: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2770543744
Thanks to Mercuttio for pointing out the secrets of the Konami code. I barely sprint and jump in stealth games, and I missed trying out these new abilities.

And finally thanks to developer FoolishPyro and team for making this short but sweet experience, while also providing the Konami Code fix. Link to discussion here.