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