I believe the scars are likely because Frankenstein’s monster is stitched out of the parts of multiple dead people.
I really like the Jekyll/Hyde theory. Frankenstein could have accidentally poisoned his brother, killing him. So he dedicates his life to finding a way to bring him back, only when he does, he’s not quite the same. We saw that Daniel still had parts of him remaining, and then he was also a monster. So the brother could be Jekyll while the Frankenstein’s Monster part of him is Hyde.
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