Why does Gragas, Esq. have mirrored sunglasses? Is this a pop culture reference I’m not missing? He’s wearing a three-piece. And he’s indoors.
Anyway, setting that mystery aside, Gragas, Esq. has a rule clarification for us.
Divinity is a 2v2 arc. Bandle City and Icathia have allied against Bilgewater and the Freljord. In matches between rivals (e.g. Bandle City versus Bilgewater), factions may be repped by their own Summoners and their ally’s Summoners. So, if you’re making a Freljord versus Bandle City match, Freljord can grab Freljord or Bilgewater Summoners, and Bandle City can use Bandle or Icathian Summoners. (Champions are determined by the factions, not by the Summoners: if you’re an Icathian helping out Bandle City, the only Void demon you’re allowed to play is Teemo.)
To put it another way, you have an “honorary membership” with your ally faction.
Conversely, if you play a match against your ally, you nullify the match, just as you would if you played against your “main” faction.
If Bandle City fights Icathia, or Bilgewater fights Freljord, i.e. if one ally fights another, then the other two, rival factions can sub for either side, though it will reduce the match value by 20% per subbed Summoner.