How about if Magica manages to find her brother and turn him back to normal, he HE becomes the main antagonist. Or maybe Merlock the Magician like from the original version's movie? He was referenced in the show.

What if like black hearns finds her lab and make clones of all the villans including po de spell that's just my thoghts

I feel like a new antagonist would be good, but more clones could be interesting. Might be an interesting way of introducing 2017 versions of classic characters, like they did with May and June.

Don carnosine? who dat