Implying of course, that Hoid is definitely bent on restoring Adonalsium. Perhaps Hoid is, or is part, of this opposition, and maybe the 'most frightening and terrible of all the Shards' is the part of Adolasium that he was opposed to? Or perhaps this is what the 'element' relates to (though I have my own, unrelated, pet theory about that). If Adonalsium wasn't all-powerful, as since it was broken, we can assume it wasn't, the opposing force didn't have to be his equal and opposite, but just effective.