World Forger is a multiversal being. He actually created every universe that ever was in DC universe by his bare hands and even in his weakened state (He can't operate at full power in 3D universe), he needed a special magical room or he would've shattered entire reality with just a swing of his hammer.
In the comic, he designed and built the new universe in the sixth dimension and, once he'd fully powered up, he would hit his space hammer on his cosmic anvil which would, in his own words, "shatter the old universe," so he could just drop the new one on to replace it.
Going by the statements, it was meant to be an entire universe and we saw earth, Apokalypse and various other planets off in deep space like Thanagar.
Checked it and can confirm. Full multiverse.
I will note, during their fight with Forger before Superman shows up, J'onn is all like "We need to get the hammer away from him," which suggests the ability to destroy a multiverse is tied to the hammer and crisis anvil rather than necessarily intrinsically tied to World Forger himself.
I think my brains have started dribbling out of my nose, reading about this World Forger guy.
“So how did you find space for the multiverse?“
“I cleared away the old multiverse.”
“How?”
“I hit it. With a hammer.
....
It’s a very big hammer.”
"At the end of the day, Arby is a pretty prolific poster proposing a plurality of proper posts for us."
- big_adventure
How much of a factor the hammer plays doesn't seem very relevant when what matters is his durability. That said, someone whose work is building universes on a forge (and therefore likely exposed to essentially a big bang) would have to be preeeetty durable. I am kind of skeptical that we take this isn't SMvsFL, but I don't know if Supes has shown other limits when sun dipped. I will say that post crisis different suns had different effects on him, including some (blue?) that powered him up more. If these particular stars built for a different cosmos have different properties, who knows what would happen?
Anyone got an issue number so I can read for myself? Flipping through the recent issues, I did find a sweet Martian Manhunter feat: telepathically contacting everyone on Earth. Then he cast his mine even further out: "faster... weaving through the invisible clockwork of the universe, between nanoseconds, zeptoseconds... planck time."
Superman's other stuff in post crisis era when sun dipped includes stuff like supposedly having enough power to overpower the Worlogog, pushing against a Warworld that absorbed the big bang and shaking the star system as a side effect of a fight with Darkseid
I suppose we can include Superman one million too where he at least somewhat gives powers to the galaxy moving Kal Kent
The World Forger stuff starts from Justice League 19
It seems like the power of a sub dipped Supes varies wildly depending on the plot. That about accurate?
I can't really think why flying through multiple stars would be better than hanging out in one star for a longer time. Unless the different stars have different properties or cause some sort of reaction when exposed to each other. It isn't like Supes drains a star dry or really depletes it all when he flies through it or hangs out in one.