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 Punchy Target mini-game.
Introduce all Camp Kids to Mr. Pokeylope.
See yourself through the eyes of many others.
Re-brain the Children.
Complete The Asylum.
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 80.
Redeem all 16 Scavenger Hunt Items.
Complete The Milkman Conspiracy.
Complete Lungfishopolis.
Achieve Rank 60.
Hear Vernon's Ghost Story.
Spy on Bobby's love life.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Achieve Rank 40.
Complete Sasha’s Shooting Gallery.
Use the bacon. A lot.
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.
Buy an item from the Camp Store on Christmas.
Read many bulletin board messages.
Discover the secret history of Whispering Rock.
Complete Basic Braining.