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