Yume Nikki contains some unused spirites.
FC World
A huge part of the FC World is unreachable. There is also a smaller island with 4 statue's that cannot be reached in any way.
Graphics for three different FC world tree's exist, but only one of them is used. Here are the other two: File:FC 01 Tree's.png
There is also a tiny little cave graphic: File:FC 01 - kopie.png
Madotsuki's Room
There is a cracked window: 
And a round pillow: File:Ƒ-ƒCƒ‹-ƒ€.gif
Puddle World
One of those Japanese...things appears in the tileset! File:…‚½‚Ü‚è un.gif
Witch's Island
The pond on Witch's Island sometimes contains some sort of sea creature. If you noclip in his pond and interact with him, then he will make noise. He can also be stabbed by noclipping in the pond.
The Pink Sea
A pink gate! Note that the Pink Sea shares the same tileset as the Winter World.
Perhaps this was meant to be the entrance to the Pink Sea?
The Lost Party Member
Another Party member can be added to your party, but this never happens in the game. It's nameless and there are no sprites associated with it. But having it in your party causes Several scripts in the game to change!
- All sane and insane Toriningen disappear! The Toriningen party and the nice lunatic in the Mall are not removed.
- The top-left cupboard in the Guillotine Room will disappear. If you stand on it's former tile and press the action button, then you will end up in front of one of the 8 cupboards in the Eye world. If you enter the world again, then the cupboard will have returned to it's rightful spot.
- If you wake up, you will be unable to move. You can still open your menu.
- The ending is not changed at all. Bummer.