In an early chapter, Hades attacks Shirou and says his wife Persephone had earlier been killed by a Campione, fueling his hatred of them. The author admitted to making that detail up for the story, then a later Campione! novel confirmed Persephone had been killed by a Campione.
Rhongomyniad started out as a barely mentioned Noble Phantasm that had its properties invented by the author as a way of showing the many different versions of the tale of King Arthur. Come 2015-2016 side material, it has been confirmed as a Noble Phantasm that's A++ to EX Rank! He basically gave a weapon stronger than even Excalibur to Guinevere!
Actually part of a supposed Gambit, since the creatures managed to steal something from the Campiones, something that can supposedly defeat them.
At the same time however the banquet ended with positive relations for the Campiones, if there is more upcoming information about this situation it can possibly culminate into a fight between all four Campiones and the mastermind.