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