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.
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.
Complete Meat Circus.
Achieve Rank 101.
Sort all Emotional Baggage.
Gather all Figments.
Crack all Vaults.
Complete The Asylum.
See yourself through the eyes of many others.
Revisit all brains after completion.
Give the Coach's speech on the stump.
Discover the secret history of Whispering Rock.
Read many bulletin board messages.
Introduce all Camp Kids to Mr. Pokeylope.
Re-brain the Children.
Complete Waterloo World.
Complete Black Velvetopia.
Earn all Merit Badges.
Find Edgar's Secret Garden.
Achieve Rank 80.
Complete Gloria’s Theater.
Redeem all 16 Scavenger Hunt Items.
Complete The Milkman Conspiracy.
Achieve Rank 60.
Use the bacon. A lot.
Complete Lungfishopolis.
Achieve Rank 40.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Complete Basic Braining.
Complete the Punchy Target mini-game.
Achieve Rank 20.
Complete Sasha’s Shooting Gallery.
Find all Golden Helmets.