"Most misborn" is a phrase that may be difficult to find synonyms for, given its specific and somewhat archaic meaning. However, there are some options one could consider. For instance, the phrase suggests that something is extremely flawed, perhaps even cursed or doomed from birth. Synonyms for "misborn" might include "malformed," "deformed," or "monstrous." To convey the idea of something being particularly egregious or disastrous, synonyms for "most" could include "worst," "most disastrous," or "most calamitous." Combined, some alternative phrases might include "the most deformed and cursed" or "the most calamitous and flawed".