Some cards refer to Autobots or Decepticons. How do I know which characters are Autobots?
[Source: WotC]
Autobots have a red frame and the Autobot insignia in the lower right corner. Decepticons have a purple frame and the Decepticon insignia in the lower right corner. A few characters have "Autobot" or "Decepticon" in their names, although these aren’t the only Autobots and Decepticons.
Different faction means "does not share a faction identity." For a character which is both an Autobot and a Decepticon, "not sharing a faction identity" means NOT Autobot and NOT Decepticon. Currently, this leaves Mercenary as the only different faction.