In this episode, R&D’s Mike Mearls discusses the creation of the fifth edition DMG—touching upon what aspects of past versions were considered, included, or revised; the importance of the playtest process to help shape the development; and criteria for what creatures and magic items made the cut.
@vikke064 Question about spells with saves and damage (eg shatter): is there any explicit rule about damage roll 1/spell or 1/target? Check out the section on damage rolls in the combat rules. You'll see that a spell like shatter has one damage roll.
— Jeremy Crawford (@JeremyECrawford) November 28, 2014