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