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