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