I'm going to start writing up things I think should be in the OP.

Dimension Shifting:
Within the grand Multiverse exist a myriad of universes. Among those who live within these realms, there are a number that have seemingly at random been granted the capability to shift from reality to reality. They can walk between the many universes of HCL, allowing them to go on grand adventures. It's these people that may eventually determine the fate of the Multiverse. However, dimension shifting isn't instant, and it isn't easy.

In order to move from one dimension to another, you must be able to concentrate. The process usually takes about a minute, and any interruptions during that time period will prevent you from transporting. There are also many magic spells, or sciency dimensional anchors that might prevent you from leaving or entering a certain reality.