Well, Godzilla can still win IMO. It's going to be a challenge, but just a glancing blow from a limb or even potentially a near miss from his atomic breath can do it. But it's managing to do so while battling the shifting and folding buildings and terrain that won't be easy at all. And, as you said, if he makes a false move, things could go horribly wrong.
this is very interesting as Godzilla has never fought someone like Kaecilius, nor has he fought in the mirror dimension... Godzilla doesn't seem to be smart, which Kaecilius will take advantage of. I'm gonna side with Kaecilius on this one. He can bend his will in the mirror dimension while Godzilla might not be able to even hit him
I don't think all sorcerers can do what Kaecilius did in the Mirror Dimension. I watched Dr Strange a few days ago again. The Ancient One specifically mentions that he's more powerful there because of his connection to Dormammu and the ritual he performed (the one that gave him and his zealots those crusty eyes). In fact, with the deaths of Kaecilius and the Ancient One, as far as I am aware, the only living sorcerer who actually has the knowledge required to siphon energy from the Dark Dimension is Strange himself (he memorised the rituals when he used the Time Stone to temporarily restore the pages, which is later confirmed, and also how he knew about the Ancient One doing so to extend her lifespan). And even then, Strange probably doesn't have the mastery required yet to siphon the energy safely without being corrupted, like the Ancient One could. The Ancient One literally had centuries more XP than the next living sorcerer.