Big Bomb is the 4th of 9 cards out of the 15 revealed for Beta 13.4 on Twitter. Like most of the others, it didn't change between reveal and release.
Big Bomb is an amazing card. Being an upgraded version of Bomb, it still kills itself at the start of your turn. But now, it also kills all other monsters on the board, making it work like Determination's Hyper Goner.
But that's not all. If it dies before your turn starts again, it will kill the monster that killed it, which will most likely be Muffet's Pet.
There are a few counters for this. Like mentioned before, Muffet's Pet is an option. However, it will die alongside the Big Bomb due to its ability, so Silencing it first with cards like Scarf Mouse or Nacarat Jester is a good idea.
Another option is by using Madjick, so its HP drops to 1. Then you can use a low cost monster to sacrifice itself and kill the Big Bomb, like Loox. You can also use a spell like Punishment or Worsening, as those will not trigger the Dust.