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