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