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