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