Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
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.
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.
Complete Black Velvetopia.
Find all Golden Helmets.
Earn all Merit Badges.
Find Edgar's Secret Garden.
Complete Waterloo World.
Complete Gloria’s Theater.
Achieve Rank 80.
See yourself through the eyes of many others.
Give the Coach's speech on the stump.
Redeem all 16 Scavenger Hunt Items.
Complete The Milkman Conspiracy.
Discover the secret history of Whispering Rock.
Complete the Punchy Target mini-game.
Achieve Rank 60.
Use the bacon. A lot.
Complete Lungfishopolis.
Hear Vernon's Ghost Story.
Complete Milla’s Dance Party.
Achieve Rank 40.
Uncover Milla's Secret.
Complete Sasha’s Shooting Gallery.
Witness Maloof's transformation.
Achieve Rank 20.
Read many bulletin board messages.
Complete Basic Braining.