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