2.I believe I heard it was stated somewhere in the manga (prolly around the valentine fight) that Act 4 was the only act 4 in the multiverse, hence why Valentine couldn't just get one with act 4 to reverse the inf rotation.
The "only one in the multiverse" was the Saint's Corpse.
But Johnny of the Saint's Corpse world was the "origin" of his infinite rotation power, and since after, as he put it, dozens of tries, dealing with
that Johnny would undo others with act 4 (as far as he knows?).
...er, how do I put a page from Mangadex itself here? Chapter 87, page 12 of the official colored?
If you're talking about him entering the pocket dimension of Funny Valentine, I thought it was just him entering a door that would normally harm people, so to speak. I don't believe he can just rip a hole and jump into a new
dimension.
That is exactly how Funny Valentine's powers work, though. Well, not rip a hole, but besides that. It
is a bit confusing (it is Araki after all), but...
Not pocket dimension. Actual reality jumping there.
As long as Funny Valentine is pressed between two things - does not even need to be related to life and death, just a piece of cloth falling on top of him can do it - he can jump between dimensions. And
only he can touch the version of himself in another dimension, even objects cannot touch the same thing in a different world.
And he can take other people and even leave them halfway through the door, something that... was an issue dealt with at least once.
Anyway, my point was not about jumping dimensions, but that parallel timelines and reality manipulation is a
major point in Steel Ball Run, to the point it is the antagonist's main power.
And I can't think of a better way of saying "and now for an universe completelly different, not just a changed past of what we had before" than by doing "this part, where the past is completelly different, we will deal with dimension hopping".