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