Board Thread:Fun and Games/@comment-27996636-20170814181056/@comment-31063493-20170819002332

Whis: 'there is a universe where lives a mortal even a God of Destruction can't defeat'

He then goes on to say that the very same GoD beat Beerus in a arm wrestling match. Beerus wasn't scared, just annoyed Whis brought it up. If the mortal was from U11, Beerus would be scared because Goku and Vegeta would have to fight him.

Either this is call back to when Whis said Goku and Vegeta working together could defeat Beerus and Goku and Geets are going to tag team Jiren or the mortal isn't Jiren and is from one of the non-participating Universes.