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