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.
Crack all Vaults.
Complete The Asylum.
Re-brain the Children.
Complete Black Velvetopia.
Find Edgar's Secret Garden.
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.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Achieve Rank 40.
Complete Sasha’s Shooting Gallery.
Witness Maloof's transformation.
Use the bacon. A lot.
Achieve Rank 20.
Buy an item from the Camp Store on Christmas.
Cook and consume two different kinds of roast in one sitting.
Read many bulletin board messages.
Give the Coach's speech on the stump.
Discover the secret history of Whispering Rock.
Complete Basic Braining.
Complete the Punchy Target mini-game.
Achieve Rank 101.
Sort all Emotional Baggage.
Gather all Figments.
Introduce all Camp Kids to Mr. Pokeylope.
Revisit all brains after completion.