That was so cringe I just ignored it, being in violation of the rules of space-time just means he broke the law, which he did, it was a cop of the Time Police who said that.
Even if that was some Space-Time Manip, which it isn't, doing some Space-Time Manip+destroying the universe doesn't magically mean all of timeline was also destroyed. If you disagree with this then go and do your own CRT about the Tiering System to try to apply this new info to it, if our standards fall that low then I may as well upgrade Jorgen von Strangle via creating a bomb that destroys the universe+tears the very fabric of time. If you still disagree but don't feel like making a CRT about out tiering then don't derail this thread that doesn't make any sense, that's trolling.
"Unknown physically and with regular powers, eventually 3-A via ripping a dimension (Had a rip into the universe Time Baby stated that, if continued, could destroy "the very fabric of existence" as visualized by an explosion eclipsing some area in space, and Blendin knew from another point in time that Bill destroyed "the entire universe" because of this event. The rip presumably started with Bill's arrival to that universe, days passed without it getting notably worse, and the destruction would be an unknown time later)"
There's a note below pointing out how Bill being a threat to the multiverse doesn't mean he's 2-A, it should below it have yet another note pointing out how Blendin knowing that the universe would be destroyed means the feat explicitly can't be Low 2-C, as the timeline isn't destroyed by it. It can also point out as supporting evidence (as it's too long for Bill's AP) how Stanford Pines was worried that Bill might destroy the universe despite how Bill only told him his delusional plan of chaotically ruling it over while causing notably less damage around in the universe, without destroying it all, meaning that Ford likely knew what Bill could cause.
As said before, pointing out the explosion shows that the destruction was likely quickly when it happened and we should point out how much time happened until his rip blew everything up, as he can't really use it as an attack.