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