Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Hear Vernon's Ghost Story.
Witness Maloof's transformation.
Complete Meat Circus.
Achieve Rank 101.
Gather all Figments.
Sort all Emotional Baggage.
Crack all Vaults.
Complete The Asylum.
Give the Coach's speech on the stump.
Introduce all Camp Kids to Mr. Pokeylope.
Buy an item from the Camp Store on Christmas.
Complete the Punchy Target mini-game.
Discover the secret history of Whispering Rock.
See yourself through the eyes of many others.
Re-brain the Children.
Revisit all brains after completion.
Achieve Rank 80.
Redeem all 16 Scavenger Hunt Items.
Complete Gloria’s Theater.
Complete Waterloo World.
Achieve Rank 60.
Find all Golden Helmets.
Complete Black Velvetopia.
Earn all Merit Badges.
Find Edgar's Secret Garden.
Complete The Milkman Conspiracy.
Use the bacon. A lot.
Complete Lungfishopolis.
Achieve Rank 40.
Read many bulletin board messages.
Spy on Bobby's love life.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Achieve Rank 20.
Complete Sasha’s Shooting Gallery.
Cook and consume two different kinds of roast in one sitting.
Complete Basic Braining.