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.
Find all Golden Helmets.
Spy on Bobby's love life.
Hear Vernon's Ghost Story.
Witness Maloof's transformation.
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.
Discover the secret history of Whispering Rock.
Use the bacon. A lot.
Give the Coach's speech on the stump.
Read many bulletin board messages.
Introduce all Camp Kids to Mr. Pokeylope.
See yourself through the eyes of many others.
Re-brain the Children.
Complete Waterloo World.
Complete Gloria’s Theater.
Complete Black Velvetopia.
Earn all Merit Badges.
Achieve Rank 80.
Find Edgar's Secret Garden.
Redeem all 16 Scavenger Hunt Items.
Complete the Punchy Target mini-game.
Complete The Milkman Conspiracy.
Achieve Rank 60.
Complete Lungfishopolis.
Achieve Rank 40.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Achieve Rank 20.
Complete Sasha’s Shooting Gallery.
Complete Basic Braining.