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