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