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