A short, but very detailed chapter here.
Back in the past, two folks witnessed Big Mom eat Caramel and the children. A giant who returned to Elbaf and told the story thus revealing why the Giants hate Big Mom even more and a young chef named Tori...I mean Strausen who helped Big Mom rise to power while using his Devil Fruit power to make delicious log meat.
Caramel inspired Big Mom to create a social justice utopia and in a way passed on the Soul Soul Fruit powers onto Big Mom. Also, Jesus Christ, Big Mom had a bounty of 50 Million Berries at the age of 6 and 500 Million Berries when she was a teenager.
Back to the present, Bege and Co. launch their gas missiles at Big Mom. Target hit, Big Mom dead, one Yonko down, let's go to Wano! Ha! Did you think this plan would work?!
As many of you predicted, the plan failed as Big Mom's yell combined with Conqueror's Haki destroyed the missiles and the escape mirror. With no where left to go, there's only one thing to do - have Bege transform into a giant castle mecha.