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