I don't think there's anything to invest in with the current Sonny and Carly. I feel the 2010s iteration of them has always been a marriage of convenience and comfort for the characters in their heart of hearts, nothing more. It could break apart tomorrow. And it's clearly the show out of ideas.
OK I will bite.
Erika Slezak had great moments as Viki.
But with the caveat I never saw her first take on the role when it was first created (and I hear this was the best version), her work as the alters was just uncomfortably bad imho. I swear that Niki is the broadest least subtle caricature of a performance she could possibly have chosen to give. I hear the argument that she was written as a caricature but I would cringe every time she came on-screen as someone else other than Viki because the scenery-chewing was just too in-your-face for me.
I think Marlena was a bit flustered and all over the place due to lack of sleep from Stefano's nightly visits and was also already possessed (The Desecrator - Marlena - burned the Horton Centre Christmas presents after Marlena finished talking to Alice).