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