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