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