Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Hear Vernon's Ghost Story.
Buy an item from the Camp Store on Christmas.
Cook and consume two different kinds of roast in one sitting.
Achieve Rank 101.
Sort all Emotional Baggage.
Gather all Figments.
Crack all Vaults.
Complete the Punchy Target mini-game.
See yourself through the eyes of many others.
Read many bulletin board messages.
Discover the secret history of Whispering Rock.
Introduce all Camp Kids to Mr. Pokeylope.
Re-brain the Children.
Revisit all brains after completion.
Achieve Rank 80.
Give the Coach's speech on the stump.
Redeem all 16 Scavenger Hunt Items.
Complete Meat Circus.
Complete The Asylum.
Complete Gloria’s Theater.
Complete Black Velvetopia.
Use the bacon. A lot.
Find Edgar's Secret Garden.
Find all Golden Helmets.
Earn all Merit Badges.
Achieve Rank 60.
Complete Waterloo World.
Complete The Milkman Conspiracy.
Complete Lungfishopolis.
Achieve Rank 40.
Spy on Bobby's love life.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Achieve Rank 20.
Complete Sasha’s Shooting Gallery.
Witness Maloof's transformation.
Complete Basic Braining.