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