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