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.
Revisit all brains after completion.
Complete The Asylum.
See yourself through the eyes of many others.
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.
Complete Waterloo World.
Cook and consume two different kinds of roast in one sitting.
Discover the secret history of Whispering Rock.
Use the bacon. A lot.
Witness Maloof's transformation.
Complete Gloria’s Theater.
Achieve Rank 80.
Give the Coach's speech on the stump.
Redeem all 16 Scavenger Hunt Items.
Complete The Milkman Conspiracy.
Complete Lungfishopolis.
Achieve Rank 60.
Buy an item from the Camp Store on Christmas.
Hear Vernon's Ghost Story.
Read many bulletin board messages.
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.
Complete the Punchy Target mini-game.