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