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