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