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