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