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