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