This game has 18 achievements to get, if you're interested. A lot of them will happen automatically as you go through the game, but not all. I recommend you play the game without worrying about achievements the first time, then try for the ones you missed on your second play-through. Watch out for spoilers as you go through this list, if you haven't finished the game yet.
Teamwork: Use both Rosa and Joey to solve a puzzle. You get this one in the first case, when you use Joey to help Rosa get the key on the boat.
Geromino [sic]: Save a ghost ... and yourself. You get this one by jumping off the speeding boat before it crashes.
Key Snatcher: Sometimes you have to rob a few old ladies... This refers to the key you take from Penelope Haines's room. In order to get the achievement, you have to get the key on the first attempt.
Out Of Sight: Get out of a sticky situation. This refers to getting Rosa out of the Haines apartment without being seen. To get the achievement, you need to accomplish this on the first try.
Check Out The Competition: Visit another psychic. You get this one when you locate and talk to Lisa Tenzin.
Dumpster Diver: Find a lost item. This refers to Jeremy's lost cell phone.
Take my Card: Use Rosa's business card for an unintended purpose. You'll be doing this while tracking down Tiffany.
Music Lover: Find Jamie's favorite song. This happens during the Jamie case.
Still Got It: Not bad, for a dead guy. This happens during the Jamie case, after Joey wins her confidence.
Unbound: Free Rosa. This happens when Rosa frees herself after she's been tied up.
Back from Beyond: Come back from the void. This happens during the endgame, when Joey finds a way to come back to the real world after being banished by Rosa.
Face Plant: Abuse an innocent. This happens in the Haines apartment. The only innocent in this game is baby Chris ... and the way to get this one is for Joey to get the baby to follow him into the next room while the door is still closed. So before you blow on the thermostat to get Madison to open the door, click on the baby and float through the door. Hey, it's okay to laugh -- the baby thinks it's pretty funny.
Button Pusher: Open the secret compartment on your very first try. This refers to the secret compartment in the yacht, the one with the knotholes.
Bullet Dodger: Escape the yacht with only getting shot once. You can make Joey talk to Ryan over and over, just because it's funny seeing him and Rosa react to physical pain; however, to get this award, just have Joey talk to him once and let Rosa handle all the conversation after that.
Ghosts of the Past: Find all the references to previous games in Rosa's apartment. To get this one, have Rosa look at everything with a hotspot in her apartment, including plants, teddy bear, and pictures on the wall.
Blowey Mallone: Use Joey's breath power on at least 10 people. Joey won't blow on everyone, but that's okay; you get credit for this achievement if you even try to blow on someone and Joey refuses. (And some of his refusals are pretty funny too.)
Medium Well Done: Complete the game at least once.
Listen Closely, Now: Play the whole game with commentary mode on (from the main menu till the end). To get this going, start the game, turn on commentary mode, then start a new game and play it all the way through without turning commentary mode off. You don't actually have to listen to all the comments; if you want to get back to the game, press the spacebar to stop the talking and get back to the game. In addition to the comments that pop up automatically as you play, there will also be large speech bubbles with C or B in them in many scenes -- C for commentary, B for bloopers from the voice-acting sessions.
This is the low-spoiler guide for "Achievements" puzzle in The Blackwell Deception. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.