As copyright (comic book) characters hail from different realities and many such characters possess powers and abilities that allow for travel between dimensions or through time, questions may arise as to how those abilities interact within the fabric of the MUX.
For pocket dimensions or realms that exist primarily connected to a single character or has limited access through a small group of characters, those realms will exist as usual for those characters. Characters will be able to travel to and from those realms as normal, however they will never be able to use those realms as a means in which to return to their 'home' or 'origin' world. Characters that teleport through different dimensions will still be able to do so, but again will always return to the base world/dimension of AI MUX.
Other dimensions and realms that exist parallel to the world and have been accessed by multiple characters - such as the Negative Zone or the Phantom Zone - may be introduced to the world of AI MUX, however this would be done so at their point of origin, and would exist as a separate iteration of those realms within the game world. For example, Reed Richards may attempt to access the Negative Zone, but would discover a 'new' Negative Zone that would not include Annihilus, and would not grant any access to the 'prime' reality of Marvel Comics.
To be frank, the administration is asking players to embrace the theme of the game and to realize that characters are fairly much 'stuck' in this new world. Attempts may be made to return to home, but those attempts will always fail and characters should be quick to reconcile themselves to their new surroundings.
On a similar note, those copyright characters that have any sort of time travel ability should realize that while they will be allowed to journey forward and backwards through time according to their abilities, no character will be allowed to alter or disrupt the timeline of the game. Events may be observed, but any attempts by characters to change the past will only result in a divergent timeline that will not affect the game itself. Additionally, that divergent timeline will be inaccessible, as when the character in question returns to the present, they will return to the game's main, ongoing timeline and continuity. There will be no exceptions to this rule.
Players are welcome to emit journeys into alternate futures, should their powers allow them to do so, but any such futures are possible futures only and will have no guarantee of ever occurring. Accordingly, knowledge gained from those futures will be unreliable and potentially useless.