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