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