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