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