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