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