Board Thread:Questions and Answers/@comment-30751547-20170205225537/@comment-103.221.71.224-20171221090749

In the manga, there is a thing called monster cell, after eating it human transform to monsters and also that if they can control the monster's body well enough then they can change the way they look. So maybe saitama accidently ate it but was strong enough to control it and became monster maybe even above god level