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