Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Complete the Punchy Target mini-game.
Uncover Milla's Secret.
Re-brain the Children.
Use the bacon. A lot.
Read many bulletin board messages.
Discover the secret history of Whispering Rock.
Give the Coach's speech on the stump.
Redeem all 16 Scavenger Hunt Items.
Complete Meat Circus.
Achieve Rank 80.
Complete The Asylum.
Complete Waterloo World.
Complete Black Velvetopia.
Earn all Merit Badges.
Complete Gloria’s Theater.
Achieve Rank 60.
Complete The Milkman Conspiracy.
Complete Lungfishopolis.
Achieve Rank 40.
Complete Milla’s Dance Party.
Complete Sasha’s Shooting Gallery.
Achieve Rank 20.
Complete Basic Braining.
Achieve Rank 101.
Sort all Emotional Baggage.
Crack all Vaults.
Gather all Figments.
Find all Golden Helmets.
Find Edgar's Secret Garden.
Introduce all Camp Kids to Mr. Pokeylope.
See yourself through the eyes of many others.
Revisit all brains after completion.
Hear Vernon's Ghost Story.
Witness Maloof's transformation.
Spy on Bobby's love life.
Buy an item from the Camp Store on Christmas.
Cook and consume two different kinds of roast in one sitting.