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