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