Here is the full list of all 30 Agent A: A puzzle in disguise achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Complete all conversations with Günther
Give your new ally their favourite delicacy, prepared to perfection
Complete Agent A in less than 120 minutes
Collect the fish bones a second time
Deliver a surprise to Onyx and you'll have an ally for life
Release your latest catch... HINT: not Ruby though
The old phone in the shoe trick eh!? Find a shoe phone
Make a 'Boing' sound 10 times quickly
Complete all conversations with Trevor
Overflow the sink a second time
Investigate Ruby's phone call records
Sabotage Ruby's submarine
Find Ruby's submarine
Give Günther (the crazy Norwegian bird) hiccups
Find every spider web in Agent A
Shoot the gun range target 100 times
Broadcast warning message to Agent B
Download Ruby's mission
Uncover Ruby's mission
Sneak into Ruby's hideout
Show us your DJ skills, scratch a record for 10 seconds
Give Agent A an 'electrifying' hairdo
Hit the briefcase kill switch
Access the hidden pool door
Disarm the electric pool
Open a stone doorway
Disable the house alarm system
Look up glissando in a dictionary, you'll know what to do Agent... HINT: start from the marked key
Locate Ruby La Rouge
Infiltrate Ruby's secret lair