[Oh, Karma regularly kicks him in the ass and dumps him head first in the trash. He knows it too. There's a reason why he gets stuck in so many frustrating realities after all. That being said he and common sense have a restraining order against each other so he continues to do what he does.]

Nothing is out side of the realm of possibility. Somethings are less probable than others but nothing is outside the realm of possibility.

[Which he knows, being a probability manipulator.]

How common... hm... it depends on the type. Alternate realities are, of course, so wide spread that you can't spit without hitting one. Pocket dimensions aren't that common, it takes work to set them up or the natural circumstances to create them are rather difficult to trigger. Nexus points are about the same, but where as pocket dimensions are rather like a slight bulge

[He draws a glowing line in the air and then adds a small nobby bit on the edge of it.]

Like that. Nexus points, on the other hand, are cross over points between various universes or realities.

[Some more glowing lines, this time crossing over each other at a particular point which he then circled.]

These, if you know what you're doing can be artificially created or they can occur naturally, as well.

This place here, I believe, is an artificially created nexus point. Beings created portals or ... something...

[Vague handwave.]

To pull others here for some reason or another.

Rather like a black hole!