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