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