WMG: Paper Mario: Sticker Star

Tatanga will be the Big Bad.

  • Jossed, sadly.

The final boss will be an Evil Knockoff of Mario.
Past final bosses of the series: a nigh-invincible star-powered Bowser, Princess Peach possessed by an evil demon queen, and an unholy fusion of Luigi and the BigBad. Now look back at Super Paper Mario: who are the heroes of the Light Prognosticus? The red-clad mustachioed plumber is next on the list.

Obviously, Mario can't fight himself, so Bowser will probably use magic to create a clone that can make him meet his match (Metal Mario, maybe?).

To make up for not having partners this time around, characters from previous games will have cameos
And if there's an arena level, at one point Troopa Jr., Lord Crump, and O'Chunks will team up against Mario 3-on-1.
  • Jossed due to Executive Meddling. Parakarry and Goombella are mentioned and Rawk Hawk is given a small nod, but no one appears.

There is a reason Bowser has no dialogue...
Chances are the crown he is wearing doesn't allow him to speak, which comes at the cost of reviving him as giant cardboard version of himself. The Royal Stickers drove their wearers to madness, Bowser's crown made him an Empty Shell.

Sticker Star is an in-universe children's storybook.
It certainly explains the inconsistancies with the rest of the series and why everyone is apparently actually made of paper.
  • On the other hand, Literary Agent Hypothesis could also apply here, meaning that the storynote  did in fact, happen, but is told in the form of the aforementioned storybook.

In the event future Paper Mario games continue down the "main games/Mario's world-only" criteria for characters, characters from newer games will appear.
For sake of example...

The Royal Stickers and Kersti are actually villains/malicious in nature.
For artifacts said to grant wishes, they shouldn't be driving their wearers crazy/mute at all. The only reason they would change the personality of their wearer would be if they were control devices.

Continuing on, notice how whenever Kersti is inconvenienced by anything, she never worries. Angry? Yes, she does get angry. But never does she worry. Why? Because she secretly controls the strings of the Royal Stickers' victims, and could probably call them off, or even order them to take care of the problem, if she made a real effort to exert control. That time Petey ate her? She was in control all along. When Bowser didn't listen to her, she wasn't actually trying to call him off or exerting any power. And what was used to defeat Megasparkle Bowser in the end? Not the combined power of the five Royal Stickers gathered so far...just Kersti.

To put it simply, helping Kersti and reviving her was probably the worst thing Mario could have done...