1. Where was the Joker during The Dark Knight Rises?
The Joker is one of Batman's most enduring villains - one of the key concepts of their relationship is that neither one can ever kill the other (Batman because of his morals, The Joker because he likes having Batman around), so they're doomed to continue their back-and-forth battle. The Joker even says this pretty much in his last lines of The Dark Knight:
You just couldn't let me go, could you? This is what happens when an unstoppable force meets an immovable object. You truly are incorruptible, aren't you? You won't kill me out of some misplaced sense of self-righteousness. And I won't kill you because you're just too much fun. I think you and I are destined to do this forever.
Yet, right after setting this up, The Joker is never heard from again. He and Batman never battle again. Hell, Batman's able to RETIRE - something that would have been inconceivable in pretty much any other iteration of Batman, simply due to the ongoing threat of the Joker. Hell, even when Bane releases every single criminal in all of Gotham - including old villain The Scarecrow - The Joker is unseen and not released. So what gives?
...other than Heath Ledger's death, obviously.
Turns out The Joker was being held as the lone resident of the brand new Arkham Asylum - rebuilt after the events of Batman Begins. To make matters worse for poor Joker, he was in solitary confinement, giving him no one to "play with." Guess even though Bane and Talia al-Ghul wanted to destroy Gotham with a nuke, releasing the Joker would have been TOO crazy for them.
2. Why can there only be two Sith at a time, as established in The Phantom Menace?
Users of the Dark Side of the Force existed in Star Wars since the very beginning - but they hadn't been given the same kind of definitely the Jedi had until The Phantom Menace came out in 1999, where it was established that there could only ever be two Sith at any given time - a master and an apprentice. This is, uh, an incredibly dumb strategy...on its face at least. Why not try to have as many Sith as possible? There's no limit on how many Jedi there can be - shouldn't you want to keep up with your enemy?
Luckily, the novelization of The Phantom Menace shed a little bit of light on this weird detail: turns out "gather as many Sith as possible" USED to be their modus operandi, 2000 years ago, when the Sith were first established. The problem with gathering up a bunch of ambitious, self-serving, betrayal-minded, Dark Siders is that they'll constantly betray and undermine and murder each other, leaving the Sith incredibly weak as a group.
One member was able to survive the first purge of the Sith - Darth Bane. Bane, reflecting on how Sith folks are - by nature - pretty much completely incapable of working with one another, decided to make the maximum membership 2. And it worked out pretty well!
3. Where does Gizmo from Gremlins come from?
Gizmo is the adorable Mogwai in Gremlins, who sadly undergoes a terrifying and grotesque birthing process every time he gets at all wet and mutates terribly every time he eats food at the wrong time. Who would make something like this? Why does it exist at all in the first place?!
Turns out, Mogwai were created as an ultra-peaceful, pacificist race by an alien scientist named (not joking here) Mogturmen. A Mogwai was to be sent to every planet in the universe in order to inspire its inhabitants to be kind and peace-loving as well (or get stolen by mysterious Chinese shopkeepers, either way). Earth was one of the first "test" planets.
Obviously there were still some bugs to work out - since all of the Mogwai birthed from Gizmo turned out to be sneaky, evil assholes. Mogturmen made the "give birth by gettin' wet" deal so that Mogwai could easily reproduce quickly and help spread the message of peace. It's never really made clear why the "no food after midnight" rule was implemented - probably just a bug that he was working on.