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