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