Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Achieve Rank 101.
Sort all Emotional Baggage.
Gather all Figments.
Crack all Vaults.
See yourself through the eyes of many others.
Introduce all Camp Kids to Mr. Pokeylope.
Revisit all brains after completion.
Achieve Rank 80.
Find all Golden Helmets.
Redeem all 16 Scavenger Hunt Items.
Buy an item from the Camp Store on Christmas.
Find Edgar's Secret Garden.
Cook and consume two different kinds of roast in one sitting.
Spy on Bobby's love life.
Hear Vernon's Ghost Story.
Witness Maloof's transformation.
Give the Coach's speech on the stump.
Discover the secret history of Whispering Rock.
Complete the Punchy Target mini-game.
Complete Meat Circus.
Achieve Rank 60.
Re-brain the Children.
Complete The Asylum.
Complete Black Velvetopia.
Earn all Merit Badges.
Read many bulletin board messages.
Complete Gloria’s Theater.
Complete Waterloo World.
Complete The Milkman Conspiracy.
Achieve Rank 40.
Use the bacon. A lot.
Complete Lungfishopolis.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Achieve Rank 20.
Complete Sasha’s Shooting Gallery.
Complete Basic Braining.