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