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