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