Board Thread:Event Help/@comment-34110427-20171227211725/@comment-32271305-20171230194718

As the description of that event says, you need units with Fierce Battle, which is a very common link among units that dokkan awaken with Dokkan medals (as opposed to story events medals). Dokkan awakening SSJ3 Goku would be a good start, because he'd share Fierce Battle with the SSJ4 Vegeta friend, and by keeping them together you'd be able to hit Vegito.