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