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