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