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