A collaboration project between multiple users of the 2ch Image Boards, Yume 2kki is one of the first Yume Nikki fangames out there. It stars a girl named Urotsuki who, much like Madotsuki, has really, really messed up dreams. Notable for being outright huge in comparison to even the first Yume Nikki, and there's still lots and lots planned.The game can be found here and updates very frequently.
Alternate Character Interpretation: Since what Urotsuki does is up to the player, this is natural. But ones particularly invoked by the game are that she's the most game savvy out of the various player characters due to the number of minigames she has, as well as being the drunk of the group, since she's the only one who can potentially drink until she passes out. And of course, the usual sociopath/depressed/suicidal interpretations.
Two of the endings imply perhaps the strangest thing of all, that Urotsuki is simply an ordinary girl who has weird dreams.
Artificial Limbs: Like with Yume Nikki, a number of effects replace Urotsuki's head with various objects. For Urotsuki, these are the Telephone, Eyeball Bomb, and Tissue Box effects.
Bad-Guy Bar: In the world where you get the Trombone Effect. The bar is practically filled with every chaser from the game and pulling the chainsaw on any of them will bring you to a secluded area. It is only accessible if you equip the Stretch Effect.
Bears Are Bad News: Teddy Bear Land, which is full of cardboard teddy bears either covered in blood, mutated or both.
Body Horror: Expected in this type of game. Some notable examples include:
The Marginal Vivid Worker, which that can grant you an effect that makes you pale, bow-legged, and bleeding.
If you stay in the hotel hot springs too long, you'll turn into a hideous black, white, and red blob-like creature that can barely move.
Call a Smeerp a "Rabbit": The blue grass area has green things called dogs. They bark like dogs, but otherwise are not dogs at all.
Cloning Blues: A room inside Block World appears to have a machine that would start cloning Urotsuki NON-STOP if you interact with the clone wired to it. Thankfully it's possible to get out of the lab in later versions of the game.
Cool Bike: Urotsuki's preferred method of travel is a motorcycle. She can even pop a wheelie on it. And ride on it as a wolf-girl.
Cosmetic Award: The wallpapers are this, serving no purpose other than to give you something different to look at when you're accessing the menu. Actually averted in the case of the effects, as every single one seems to either serve a purpose, get a reaction from at least one NPC, allow access to otherwise inaccessible areas, and so on. Some can actually directly lead to gaining other effects.
Creepy Doll: A clown-summoning faceless one can be found in the Circus Tent.
Cruelty Is the Only Option: There are some instances in the game where you have to kill NPCs to get past them. Also, you can't interact with Aoshiru without killing him.
The Dev Team Thinks of Everything: Going along with the staggering size, there isn't a single useless effect in the game, even if some serve much less of a purpose than others. Also notable is that an English speaking member of the dev team is actually asking for feedback on the game on Uboachan.
Dual Wielding: Not in the conventional sense, but the Wolf and Motorcycle effects can be used one after the other to allow Urotsuki to ride her motorcycle in wolf form. It not only gives her the same speed boost but also lets her howl while on the bike. There's also others planned in the future.
Dummied Out: Lots and lots of stuff, mainly content still in development, and the debug room so it can't be accidentally stumbled upon during normal gameplay.
Half The Girl She Used To Be: Happens to Urotsuki when she goes into one of the rooms in the Fake House. Played entirely for humor, as she can still walk around and there's no blood or gore associated with it.
Hikikomori: Urotsuki, in tradition to the original game.
I Can't Reach It: Urotsuki would refuse to swim across a body of water, even though she has no problems going underwater or in a hot spring.
Invisibility: An effect with two states: Barely visible, and completely invisible except for shoes.
Jump Scare: In one area, there's a pair of pillars that represents a doorway to an area that instantly transports you to an area with much more tense music and things running around extremely fast. There's no danger in this area, but the sudden change is enough to shock.
There's a chance that if you turn on the TV in Urotsuki's fake room, you will be greeted by basically all the chasers in the game with no place to escape. Though there's always the Medabomb Effect to handle that.
Don't investigate the lamp in the circus tent if you fear clowns.
Killer Sheep: A seemingly harmless lamb beheads Urotsuki if you try to kill it.
Kill It with Fire: The Lantern Effect could be used to burn NPCs that are blocking passageways.
another has her actually make the jump....but she turns out to have been a prize in a UFO Catcher (prize grabber) machine....yeah.
the third has her pinch herself awake while 'awake' in the real world. She wakes up yet again, and is on the floor with a pile of books. Implying the whole thing was a literature-inspired dream-within-a-dream. All of these have different ending conditions, of course.
the fourth, recently added in the newest edition has her setting up the staircase, and then....a train pulls up to her balcony, and a black creature onboard beckons her on to the train, which then departs.Ehhh?
Noodle People: The Tall Effect, in addition to the NPCs that display this trope.
Obvious Beta: Moreso than most fan games. Gameplay-wise, you'll find lots of paths that are blocked in some way and lack warps. The title screen itself even has a 'this game is under development' message.
Many areas that are not currently being worked on also tend to fall under the radar, and as a result feel very self-contained since they don't lead anywhere else. More recent areas tend to avoid this and feel more interconnected with the world as a whole, though.
Outside of the game, there's an insane amount of placeholder maps, events, etc. that have no content whatsoever, as well as incomplete and under development maps. No one would even know about the ending if it wasn't present in the maps and accessible via debug.
Old Save Bonus: If the game detects an older save, it will update it as well as possible to avoid problems with things not existing, being changed, and so on. So no having to get everything again/abusing the debug room.
Soundtrack Dissonance: In the brightly colored Mushroom World, there is a warp to an alternate Mushroom World with much a much darker appearance, with bloodstained mushrooms, some of which have an eye for a cap. Both worlds have the same cheery music.
Swiss Army Effect: A number of functional effects serve more than one purpose. The fairy effect grants flight and allows Urotsuki to enter small openings. The lantern provides light and can be used to kill various NPCs. And of course, all effects cause NPCs to react in various ways, some more than others.
Under the Sea: A couple of different areas are completely underwater.
Unlockable Content: Various wallpapers for Urotsuki's computer as she gets to certain points/activates certain events, among other things.
Video Game Cruelty Potential: Every single bit as present here as it is in Yume Nikki. There's also a number of events where Urotsuki can do some pretty mean things.
Video Game Cruelty Punishment: There's an area where you can cause a person in a well to fall to their death by cutting a rope. Doing so will bar any other way out and get you chased by countless monsters until some come at you from the front, which forces you awake.
There's also the sheep, as mentioned in the Killer Rabbit entry.
In the Japanese Ghost Village, if you kill the person who gives you the broken arm effect, the area becomes filled with the shadow ladies.
In the forest area, if you hurt the sane Shadow Lady there, escape down the hole, and return, the forest will become filled with malevolent Shadow Ladies and will be dark.
Killing Megusuriuri will cause the Eldritch Abomination in one of his cabinets to fester and mutate his office and Box-chan. After seeing this, you can never enter the office or see Box-chan again.
In an area close to that, stabbing an eyed creature can transport you to a place with a giant head with a very hyperactive eye laughing, and you will wake up after a while there.
If you chainsaw the clown in the building of the Guts World, it will mug you. If you don't have enough money, it will send you to the creepy head room as mentioned above.
If you try to chainsaw the man in the fox mask, he will Flash Step behind you; he might counter attack and send you to an isolated area.
Violation of Common Sense: In the Circus of Fear above, you have to first traverse a long corridor that contains hallways with a statue of a chaser in the middle of each. Even if you have no idea what is about to happen, you know it can't be good, especially when you get to the end. Clowns stop you from leaving, though.