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