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