There are 5 achievements tied to completing the 5 Acts of the game. Act 2 is roughly 50% of the total game.
There are no hidden achievements in Act 1 (that I have found)
First Trust - During your first cutscene at the apartment with Renee, make choices showing that you trust Renee.
Not Born Yesterday - During your first cutscene at the apartment with Renee, make choices showing that you doubt / are suspicious of Renee. (credit to Pride Charm)
Enabler - In Gastown, before the fake truck arrives, give cigarettes to kids out front of the Den (right from the start), and don't tell them that cigs are bad.
Sins of our Fathers - In Gastown, before the fake truck arrives, tell the kids what their parents are eating (credit to Pride Charm) (will update this with more details when I earn it)
Trout Talker - In Gastown, at the Liquor Store, talk to the Tuna 25-30 times. It will eventually explode.
Tonic for the Soul - In Gastown, at the Liquor Store, reassure Louis in your dialogue choices.
Bad Medicine - In Gastown, at the Liquor Store, be mean to Louis in your dialogue choices.
Badge of Honour - In the West End, when speaking alone with Henry, let him hold your detective badge.
Howard Lotor - In Act 1 and Act 2, tell the truth about who you are (Howard Lotor) during every conversation.
Wallace Brotor - In Act 1 and Act 2, lie about who you are (Wallace Brotor) during every conversation.
Brollace Howtor - Swap back and forth between being Howard Lotor and Wallace Brotor when speaking to people in Act 1 and Act 2.
Snoopy Snooper - At Rose's house, on her computer, look at every file.
Keep the Hope Alive - After leaving Rose's room, but before leaving Rose/Florence's house, speak with Florence again and reassure her with your dialogue choices.
There are no hidden achievements in Act 3 (that I have found)
Geezer Pleaser - In Act 2, pet the geezer. In Act 2, be nice to the delivery geezer and tip them. In Act 4, be respectful to the geezer under the Bridge, and then pet the geezer.
New Habits Die Easy - Rat out Joshua to Roger that he's smoking in the woods.
Blurb Herder - Read every bit about every book in the game, from all shelves and NPCs. The achievement will trigger when trapped in the container, after the cutscene where you're experimented on, and you read the front cover, middle, and back cover of the book left for you.
There are no hidden achievements in Act 5 (that I have found)
Missing, to be Found
Affirming Flame - "Life is harsh, but you didn't let that stop you from being compassionate when it mattered"
Smell-o-Vision - Sniff everything that can be sniffed. I thought I did this in my playthrough, but must have missed 1. If anyone has a full list of sniffable items, that would be great!
True Connection - "You felt a true connection to Renee, and acted on it."
Cruel to be Kind - "Sometimes folks need tough love. Or in your case, all the time" - Be mean / blunt to everyone throughout the whole game?
Me Time - "You chose to spend your time under the Bridge in quiet reflection" - During Act 4, don't talk to people and just interact with nature?
also, if anyone has a list of all Book locations for Blurb Herder, I can update that to include all locations. i recall at least the book store in Gastown, the bookshelves in the Minister's house, and the book in the container.
Hope everyone enjoys the guide, and thank you to anyone who helps contribute. You will be properly credited. -Tass