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