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