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