Forgot to reply earlier, was going to test out combos per your lead but got side tracked. 'Black Magic' was one of those decks I found in my early oetg days before knowing the landscape of decks including 'millcat'. Black Magic is really a variant of 'millcat'. Now, I would know to post the deck to the main millcat thread as a 'variant'.
Thematically, I would consider black magic beyond the immo+embezzled cat combo. But then to further define it, it probably needs to be darkness + fire vs. something like plaguecats. I like Wicked, Immo, and Cat serving as a the core for black magic, with or without embezzle.
Given embezzle nerf, moving millcat towards other deck type with mill as splash element is likely needed. Keep exploring. I'll get back to this 'favorite' deck at some point.