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