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