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