Two or more dimensions have decided to exist simultaneously at the same place, or other dimension is bleeding over into another. Usually involves alien flora, fauna, and other strange things to be sighted, one may even question their sanity, and so on.
Alternate names: Dimensional convergence, Dimensional invasion, Hell on Earth
The first video game about Dimensional breach was released on March 1999.
* Laws of physics become jumbled, following either completely or partially the ones present in the other dimension instead of the local one.
* Alien flora and/or fauna somehow spreads to the other dimension (but only near the breach).
* Geography changes to match that of the other dimension, seeming out of place, strange, or even alien.
Any case where one dimension, world, or some such somehow appears merged with our own without any clear source and often lacking any cause. Often the other dimension involved happens to be Hell or other place very easily likened to it.
The area affected by this effectively becomes a sort of a twilight zone between two worlds, where in some instances travel between the two may even be possible (though not necessarily so). Alternatively another dimension "bleeds over" into another.
May appear together with dimensional travel, though neither implies the other.