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