Integration
Integration is how we describe the incorporation of source materials into MCM's setting. Individual settings are called themelists, and you can view a list of them by typing -> +themelist <- on the MUSH.
Unification
When a theme is integrated, it is brought permanently into the Multiverse in a process called Unification. Unification transports at minimum all of the themelist's locations of significance, though more frequently the entire theme's world comes with it. Once a world is Unified, it exists within a discrete physical location on or around the superplanet, accessible by normal travel and by warpgate. Alternate planes and dimensions attached to inherently Multiversal themes come with it, and are likewise accessible, though they may end up scattered around the Multiverse rather than all in one place. In most cases, characters Unify with their theme, but where necessary, a character might enter into the Multiverse at some other, random point, possibly without knowledge of where their world actually is. All characters with an integrated theme have their world somewhere present in the Multiverse, though they need not define where, or even pay any attention to it if they have no desire to return to it.
Warpgates
All themelists are automatically linked to a central feature of our setting, the Warpgate Network. Warpgates begin to open within a newly unified world in short order, and they're exactly what they sound like: Points where it is possible to near-instantly travel between other warpgates. All themelists end up with at least as many warpgates as public points of interest, minimally as common as major airports.
Natural warpgates are impossible to destroy, but artificial warpgates can be constructed and destroyed.
Language Barriers
For reasons unknown to the Multiverse at large, denizens of the Multiverse inherently understand everyone else whether they speak a common language or not. The language being spoke doesn't change, and listeners can recognize that, but understand with complete clarity. This extends to common written language, but written language translates less consistently than spoken language.
Universal translation doesn't extend to secret, code, or dead languages. If it's narratively important for a language not to translate, it doesn't have to. Player characters are required to know at least one language that translates.
Spiritual Policy
In the interest of avoiding primacy conflicts, MCM dictates the existence of souls and disposition of the afterlife. Summarized: All sapient life has a soul, souls can't be destroyed, some life-after-death exists that can only be taken away by willful action by the individual. Voldemort can maim himself into a spiritual quadriplegic, but the Soul Annihilator can't wipe you out of existence.
The powers of Deities and similar beings end at the borders of their own worlds. To the extent that it matters, some form of ambiguous meta-deity has spiritual authority over the greater Multiverse, but is not an active actor.
