Cosmos

The general idea is nailed down, details are flexible.

The cosmos is seperated into the "real world" that people will be fairly farmiliar with, and TwinWorld. The door Oswald installs is one of the few pathways between the two, though the Fay and Zarth can occasionally make other portals and temporary connections.

There may be other worlds as well, but currently only Earth and TwinWorld are conceptualized.

Transporting material between worlds

Since TwinWorld is a rather metaphorical place, materials transported between worlds take on a somewhat metaphorical transformation.

When transporting materials from TwinWorld to Earth, everything carried is changed into mundane and fairly useless stuff. Twigs, dry leaves, soil, old tin cans, coat hangers, rusty cogs. This lends to the "imaginary" quality of TwinWorld, since anything brought back would have a resemblance, but not the function, of it's former self in TwinWorld.

When going the other way, from Earth to TwinWorld, everything becomes just a bit more whimsical, pure, and un-encumbered. Excess material is shorn away, magical and mechanical means replace technological ones, minor decorations grow, sometimes becoming the main form. Metal (an especially dangerous material for Fay) is maintained, and sometimes transmuted into a more potent alloy. Mostly functional Zarth equivelants are usually rendered for technology.

Idea! Mostly equivalent Fay enchantments are rendered for relationships, whether friendship or rivalry! Could have some interesting story repercussions!

There is a lot of lore about fairy treasures turning to leaves and acorns when the fairies have left. I think the permutation of transported materials could mimic this effect well.

Story ideas for this mechanic

Sometimes materials shuttled back and forth consistently change into the same thing. Other times it varies.

• It would be fun to have a short scene where Oswald experiments with a bowl of rice, going back and forth to and from TwinWorld with the bowl changing respectively into a stone bowl of tiny clouds, a plastic bowl of marshmallows, an opal bowl of pearls, a glass bowl of marbles, a crystal bowl of round rocks, and finally a bowl of ice filled with dirt. He could cry at the end.
• For bonus points, this mechanic could eventually cause a "transportation transmutation permutation conflagration instigation castigation" (someone gets chewed out for starting a fire by carrying something across the boundary of worlds)

Questions

• What level of awareness do people have in the "real world" of Faierie?
• What level of weirdness goes on in (or leaks into) the "real world"?