Arcades Sabboth

Arcades Sabboth was a mysterious figure from the Elder Dragon Wars. An Elder Dragon himself, Sabboth was one of the victors of the war, along with his brothers Nicol Bolas, Chromium Rhuell, Palladia-Mors, and his cousin Vaevictis Asmadi. He presumedly died in a battle between the planeswalkers Leshrac (who summoned the dragon) and Kristina, who killed him.

In the Ice Age comics, during the Summit on the Null Moon, planeswalkers are recalling their conflicts. Ravidels said, that one century earlier Lesrac had summoned brother of his friend Chromium to his side, during his duel with Kristina. Kristina admitted she killed the Elder Dragon in that duel.

It doesn't say clearly which Elder Dragon was summoned, only it was Chromium's brother. But,

• There were six Elder Dragons: Nicol Bolas, Chromium Rhuell, Arcades Sabboth, Palladia-Mors, their cousin Vaevictis Asmadi and Piru.
• Chromium was present on the Null Moon; Palladia was female; Piru was killed in Dihada vs. Dakkon duel; Asmadi was their cousin. They are out.
• We're left with Arcades Sabboth and Nicol Bolas. Considering pre-rev only (Nicol Bolas and Sabboth were never mentioned in stories directly), it is more likely that Leshrac would summon Nicol Bolas - they match better in colors (and against Kristina's green), but of course, Nicol Bolas was extensively used in later stories, so we have to assume it was Arcade that was killed in the duel.

That's all what is known on that matter so far.