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