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