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