- Bonus dresses
Successfully complete the indicated chapter to unlock the corresponding dress:

Silk Maiden	Oriental Grove (Chapter 3). When equipped, your enemies drop twice as many teeth.
Royal Suit	Queensland (Chapter 4). When equipped, your health is limited to four roses total.
Classic	Infernal Train (Chapter 6). When equipped, you will regain health when shrunk.
Misstitched	The Dollhouse (Chapter 5). When equipped, your Shrink Sense duration is doubled.
Siren	Deluded Depths (Chapter 2). When equipped, your enemies drop twice as many roses.
Steamdress	Hatter's Domain (Chapter 1). When equipped, breakables drop more teeth and roses.

- Psychonauts reference
In Chapter 4, just after you do the first chess puzzle, you will get chased into a hole by the giant unbeatable card monster. When you first get down there, go a short distance ahead, and look at the right wall to find a heart stone. Shrink down to learn that it is a fake rock. Run into the keyhole tunnel. On the other side is a floor where you can use a bomb to break it. Do so, then go down the stairs to get a memory and some extra teeth. There is also a skeleton sitting on a chair. It is Raz from Psychonauts. He can be identified by the red goggles, his shape, and the position he is in (which is the stance he uses for a mind attack). With this in mind, it looks like Raz is dead, and there will be no Psychonauts 2.

- Easy 'Level-Headed' achievement
Successfully complete the game, then select the final chapter, and go directly to the Boss battle. Overcome the Boss without using Hysteria to get the 'Level-Headed' achievement.

- Achievements
Do the following things to obtain the corresponding Gamerscore points:

10 Points
Eyes on the Size	Find the hidden Shrink Sense Decal.
Dress-Ups	Equip a Different Domain Dress.
Grandmaster	Finish a Chess Puzzle without failing.
Nothing Like the Smell of Bacon	Pepper All Snouts in a Chapter.
Venting frustration	Pay 7 minutes on steam vents.
Skool-Leaver	In American McGee's Alice, complete Fortress of Doors.
Weapon Schizo	Hobby Horse to Vorpal Blade to Hobby Horse Combo.
Family memories fond and faded	Find all Liddell Memories.
Out of the Woods	In American McGee's Alice, complete Wonderland Woods.
Madness Begins	In American McGee's Alice, complete Village of the Doomed.
Dead Hatter	In American McGee's Alice, complete Behind the Looking Glass.
Shooting the Moon	Acquire 4 Jars of Rose Paint.
Royal Approach	In American McGee's Alice, complete Queen of Heartsland.
The End of Daze	Finish Wonderland Chapter 5.
Grind 'em All!	Kill 5 Bolterflies sequentially with the Pepper Grinder.
Tea Party	Destroy 10 Ruin Barriers.
20 Points
Brollyant	Kill 10 Bitch Babies with Deflection.
52 Pick-Up	Overcome 52 Card Guards.
No quarter! No mercy!	Overcome 100 Ruin Enemies.
Beware of the Lagomorph	Kill 30 enemies with the Clockwork Bomb.
Ship of Fools	Finish HMS Gryphon without taking Damage.
Just peachy	Acquire all Peaches in the Scroll of Destiny.
The Beginning of the End	Finish Chapter 1 on Nightmare Difficulty.
That's Using Your Head	Finish Off With Her Head Part 2 in under 6 minutes.
25 Points
The Strong Survive	Finish the game on Easy Difficulty.
30 Points
Pulling Strings	Overcome the Dollmaker without taking any damage.
Painting the Town Red	Finish all Radula Rooms.
Seasoned Campaigner	Pepper All Snouts in the game.
Everything fit to remember	Find all Memories.
Cold Arms, Cold Heart	Overcome the Drowned Sailor without taking any damage.
Calm In the Face of Death	While on your last Rose, kill 5 Enemies without activating Hysteria.
50 Points
The Imaginative Endure	Finish the game on Normal Difficulty.
Full Recovery	In American McGee's Alice, complete the game.
Level-Headed	Finish the game using Hysteria only once.
75 Points
The Persistent Flourish	Finish the game on Hard Difficulty.
80 Points
Madness Prevails	Finish the game on Nightmare Difficulty.

10 Points
End of Innocence	Finish Vale of Tears.
When Worlds Collide	Finish Wonderland Chapter 3.
The Harder They Fall	Finish Wonderland Chapter 4.
Death by Darjeeling	Acquire the Teapot Cannon.
Strike a Deal	Improve a Weapon.
Snicker-snack!	Acquire the Vorpal Blade.
Ground Pork	Acquire the Pepper Grinder.
Grim Folly	Finish Wonderland Chapter 2.
No Happy Returns	Back to Wonderland.
Strange Hobby	Acquire the Hobby Horse.
Hatter's Demise	Finish Wonderland Chapter 1.
Neighslayer	Hit 4 Enemies With a Single Hobby Horse Ground Smash.
20 Points
More than a Mouthful	Fully upgrade a weapon.
30 Points
Armed to the Teeth	Fully upgrade all weapons.

- New Game + mode
Successfully complete the game. You can now begin a second playthrough with your previously upgraded weapons and clothes.