My Paper Mario × B3313 project... Here's the basics:

• Takes place after Super Paper Mario. Sticker Star and games after it are not canon to this universe (I haven't played them...)
• Mario has been isekai'd against his will again, this time to a dimension known as the Eternal Kingdom. He's not the first, as many people have been sent there, but he's part of the latest group of 'heroes'.
• The Prince of the Eternal Kingdom has been summoning people from other dimensions to help protect the Kingdom from destruction, as an evil faction known as STORY4D has recently risen to power...
• Time is running out. If STORY4D is able to completely destroy the Eternal Kingdom, then... No matter what happens next, the universe will be irreversibly changed.

Background Lore

Setting

The Eternal Kingdom, a dimension above normal reality, has existed since the dawn of life. Its native residents represent abstract concepts, while the Kingdom as a whole is a manifestation of dreams.

The Kingdom is alive in a sense. The center of it, home to the Eternal Castle, is unchanging; the rest of the Kingdom is made up of blurry concepts that change and morph over time. These areas always have the same general theme, but their layouts and inhabitants are not static.

The farther you get from the Castle in any direction, the more dreamlike and nonsensical the Kingdom becomes; a town near the center of the world might be similar to ones you've visited in the past, while one much farther away may not resemble a town under any definition (for example, a field with drawings of houses carved in the ground).

In the Castle's basement is a door leading to the underground portion of the Eternal Kingdom, which is chaotic and nonsensical no matter how close you are to the world's center.