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