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