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This article contains plot details from the latest books.
Marrow Regenerator is a medicine that Elwin had used for both Sophie and Fitz's injuries in Flashback. It helps to replace marrow in your bones and heal breaks and fractures. With the more potent version being used for Sandor's Mount Everest injury, it can be assumed that the regular extent is not sufficient to treat such injuries. It is not to the liking of Bullhorn as he had avoided Elwin for three days after he brewed it. The regular version of marrow detonator is more potent with the more provided, as shown through Elwin's concept of giving Sophie more to make up for the regress in progress with her thrashing.