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