Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
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.
Complete Black Velvetopia.
Find all Golden Helmets.
Earn all Merit Badges.
Find Edgar's Secret Garden.
Complete Waterloo World.
Complete Gloria’s Theater.
Achieve Rank 80.
See yourself through the eyes of many others.
Redeem all 16 Scavenger Hunt Items.
Complete The Milkman Conspiracy.
Achieve Rank 60.
Buy an item from the Camp Store on Christmas.
Witness Maloof's transformation.
Complete the Punchy Target mini-game.
Read many bulletin board messages.
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.
Hear Vernon's Ghost Story.
Complete Lungfishopolis.
Use the bacon. A lot.
Uncover Milla's Secret.
Achieve Rank 40.
Spy on Bobby's love life.
Complete Milla’s Dance Party.
Achieve Rank 20.
Complete Sasha’s Shooting Gallery.
Complete Basic Braining.