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