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