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