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