Abaddon is a third Entity.
"I won't spoil the conclusion if you're eager to see this through."
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As Eden and Zion approached earth, Abaddon asked to exchange information with Eden. Following their exchange of shards, Eden became distracted and crashed into several earths.
Doctor Mother mentions that the shards Eden obtained during the exchange (referred to as a "foreign element" in Arc 29) tended to yield more potent powers when administered to Cauldron subjects.
Contessa's shard is still actively linked to Abaddon.