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