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