Akise's actions in Mirai Nikki: Paradox gains new context when you take into account that he is an Artificial Human created specifically to observe and record the game for Deus.
Way back in Chapter 1, when Yuno knows that Yuki might stab her with the dart, she seems totally indifferent about that, pins him against a wall, kisses him, and says "You didn't stab me.", as if she knew ahead of time he wouldn't, even though her Diary wouldn't be reliable against Yuki in a fight against him. Of course she would know... She's been through all this once before and doesn't need her diary to be able to predict Yuki's reaction.
Heck, a lot of Yuno's behavior can be explained keeping this in mind:
"How can she talk about killing someone so easily?" It's not exactly like she's new to it.
Yuno suddenly deciding to meditate in Yukiteru's house to find Fifth's diary? She wasn't just trying to put herself in his shoes, she was trying to remember how he had hidden it before.
There's another layer to that bit. It would make sense that she forgot the location since she never planned on going back in time in the first place. She thought she would never have to fight him again and therefore didn't bother to remember where he hid it.
Yuno's surprise at Yukiteru's friends betraying him in Minene's attack on the school? It was one of the earliest events in her timeline, and it occurred roughly 90 days ago to her. You try remembering exactly what happened on a specific day three months prior. Not only that, but since this was also her first replay of the game, she had no way of knowing for sure that things would pan out exactly as they had before. And what's more, we have no idea what exactly happened during Minene's school bombing in the 1st world. For all we know, it could be that in the 1st world Yukiteru's schoolmates decided to protect him and not to sacrifice him, and Yuno actually expected that the same thing would happen in the 2nd world.
Her immediate suspicion of Tsubaki's motives? She knew they had been betrayed before, and tried to persuade Yukiteru.
The only reason why she probably couldn't use all of her previous knowledge to her advantage is because to maintain the illusion that she was "this world's" Yuno, she couldn't look like she knew too much beyond what information her diary gave her. And since her diary only gave her information about Yukiteru, she could only weakly justify her judgements with "Yuki will be in danger if Yuki does that."
It should be noted that the above are rendered half-moot by the fact that when Yuno-1 transmigrates to timeline-2 that most of the series took place in, she and Murmur sealed/erased a bunch of her memories for some vague, half-hinted at reason. She still obviously has flashes of past occurrences (keeping in mind she also willingly erases portions of her memory AFTER that as well), but on the whole she doesn't know most of the events as a 2nd loop in the manner of, say, Higurashi or Umineko because she doesn't have the memories anymore.
It still seems to be a case that the first Yuno was changed and affected in some way by the first survival game. The second and third Yunos don't seem anywhere near as violent as the first because they haven't actively killed people. In other words, the 1st Yuno was Conditioned to Accept Horror, the scars and mental changes made to her by the survival game, along with seeing Yukiteru die and being unable to bring him back, and possibly the fucked up nature of killing and replacing her second self, even if she wiped the memories of the events that brought about those changes.
The ending makes complete sense if you just remember who they were going to replace.
Why did Mur Mur get hit by Akise's bike, steal the bike's seat, and ask to be taken to a amusement park? Because having already gone through the events of Paradox she knows that Akise is a threat to her and Yuno's goals. So she decides to stall him as much as possible.
At the end of the first opening, and in several bits of the second feature Yuno going Ax-Crazy with what appears to be another Yuno and then fusing with her. While at first glance this may look like your typical random Anime opening moment, it becomes a great form of foreshadowing when you consider future revelations about Yuno.
This might be a little coincidental, but the first opening and ending themes perfectly capture the essence of a yandere (especially considering that one of the main characters is the defining example) with the opening being crazy, hectic, creepy and psychotic, representing the "yan" part, while the ending is more calm, representing the "dere" part.
Yuno's memory edits. Let's look at it from her perspective. She just traveled back in time and killed her other self, to prevent Yukki from dying in the end, and to finally "come together" with him. The key is, the first time, things actually went mostly right. She and Yukki were the last survivors, and they cared about each other, but they screwed up in the end and they apparently didn't get as close as Yuno wanted. So she would want to not remember things that would change this. But she had to remember the gist of why and how she came, and she had to remember her love for Yukki to further it. So she keeps those things, and because she keeps those, she risks causing some changes, and so she gives herself some other memories to keep an advantage in the game: seemingly the knowledge that they would end up fighting Fourth, Fifth, and Sixth, as well as perhaps some fighting skills. The result? Someone who knows things, particularly that she loves Yukki and needs to protect and come together with him, but yet she doesn't have a complete idea of why she knows them. In other words, as deranged a Yandere as she turns out in the time since.
Everything seems fine in the end with Yuno and Yuki being reunited and becoming God together. That is, until you start to wonder - Did 3rd world Yuno have to play the game as well? And does that mean she killed 3rd world Yuki? Not to mention this means that everyone from the 3rd world is dead too...
Considering that Deus picks them as his successor, probably not. The whole point to the game was to find a successor, after all.
There is a panel with the 3rd-world 11th specifically telling Deus that he's canceling his plans for a "Future diary game." Also it's presumed that 3rd-world Deus came and found 2nd-world Yuki and 3rd-world Yuno to replace him before the 3rd world could end.
However it could also mean 4th world Yuki and Yuno would play the game identical to the 1st world which would send 4th world Yuno to the 5th world which would result with Yuno commiting suicide, Yuki becoming God of the empty 5th world (identical to the 2nd world) and the 6th world would be a perfect world identical to the 3rd world. Then 7th world Yuki and Yuno play the game identical to the 1st world etc. This loops indefinitely...
its kinda rendered moot since its shown that the creation of an alternate timeline requires time travel back to the past and now that the survival game has been cancelled with yuki and yuno taking up the God mantle in the 3rd world no one needs to go back and with that the loop is stopped .
But what happened to the Yukiteru of the third world?
Oh hes fine, last seen walking with his parents and he got together with his first crush.
Minene shows that there can be two of one people in any given world, and Yuno is in another world with another Yuno for about 30 seconds. Even the usual Time 'rules' such as 'The you of this world can never met the you that is a visitor here.' don't apply, since what Yuno did to her 2nd world self is basically the logical opposite of this world. Given that there can be two Yukiteru's, Yukiteru of the 3rd world can have a happy life with Moe Wakaba, but Yuki's parents were the riving force for him to play the game until the end in the first place. Also, our 2nd world Yuki is God now, as well as Yuno. I personally think that since Yuno had her memories transferred into her 3rd world self and prevented her parents abuse and eventual death, Yuki would probably follow suit and either absorb his 3rd world self or make himself the Yukiteru that is with his parents. 3rd world Yuki would then cease to exist. Yuki knows this all to well an he wouldn't kill somebody knowing they can't be brought back, as shown in part by his refusal to stab Yuno. Therefore, to get a happy ending for all, 3rd world Yuki [And Yuno, probably.] must exist as another person. Due to the Mangaka stating in an interview that Yuki and Eiji are 'Closer than you think' to each other, its now a popular theory in japan that the 3rd world Yuki and the 3rd world Yuno were given new identities in order for the Yuki and Yuno we know to be with their parents. Which identities did they assume? Eiji and Rin, also in Japan and the leading protagonists of Esuno Sakae's new series, Big Order.
In the end of the manga, Yuno syncs her memories with the 3rd world Yuno to reunite with Yukiteru. 3rd world Yuno was sane, had lots of friends and actually had a functioning and healthy relationship with her parents. 1st world Yuno took away the healthy relationships, essentially destroying the 3rd Yuno's individual self.
Given that gods in this series are shown to be able to edit the memories of themselves or others (with Yuno as a good example), take into consideration just how Deus became Yuki's "Imaginary" Friend. In other words, he quite literally entered Yukiteru's mind and manipulated his memory so Yuki would remember himself as thinking Deus up. And the manner of howhorrific that might have been in practice only adds to it.
In episodes 13/14 of the anime, the deathtrap meant to kill Akise, Mao, and Kousaka was changed from a room filling up with cement to a room filling up with gas. They manage to escape by having Kousaka crawl through the air vent to the control room where Yuno, Yukiteru, and Hinata are, and having him unlock the door from there. That gives me two questions, though. First, how is the gas supposed to fill the room if there's an air vent? And second, why would Yuno use gas when the air vent in that room is also connected to the vent in her own room (which means it could be a threat to Yukki)?
That depends on what kind of gas it is. Chlorine gas, for example, is heavier than air, so the gas would collect at the bottom of the room instead of diffusing through the air vent.
Why was Yuno able to open the sealed vault? Sure, she was the real Yuno from the first world — but she was still adopted even in the first world, and there's no particular reason why it would have been designed to open for the adoptive daughter of its creator. There were two reasons why the mayor thought she wouldn't be able to open it, and her backstory only answers one of them.
That might be a bad reason, but that was the reason, also an adopted daughter isn't any less to most parents than a biological one, so that hardly matters. Maybe they wanted her to succeed the bank one day or have someone be able to open it in case of an emergency?
The Future Diaries predict the future up to 90 days. This should be more than enough time for any competent Diary User to find a DEAD END, but most of them are caught off-guard, and some don't even have time to see the DEAD END.
It is because the actions of diary users keep changing the future - the only predictions that stay valid for 90 days are those that would come true regardless of any diary user's actions. The dead end warning is only displayed once the user's death becomes almost certain.