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