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