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