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