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