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