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