The Substance is a better adaptation of Jekyll and Hyde than 99% of the adaptations out there

because such a key component of the book is that he does this to himself on purpose. He 100% wants to be split in two and do his unnamed ‘vices’ while in his Hyde persona.

and of course he regrets it when everything gets out of hand and he can’t stay in the form he wants anymore, but the initial transformation was a complete success and exactly what he was aiming for

anyway no more innocent victim adaptation-Jekyll who didn’t know what he was getting into. More Elisabeth who absolutely knows what she’s getting into and initially is very satisfied with how things are going