Huh? What do you mean by that? I didn't see anything like that in the story.
This is an inference; It's entirely
possible that Jace just ended up here randomly, but I like to think that Bolas sent Vraska here before Hour of Devastation; her having a crew and everything makes it sound like it occurred much earlier in the timeline. I also think Jace is a better mind-mage than even the story lets on - and that he pulled a piece of important info from Bolas' mind before he got wiped, and used that before he planeswalked to at least set him on the path to ruining Bolas' plans. It makes sense to me.
I'm assuming that whatever is in Orazca is part of whatever Bolas wants to use to fix the Planar Bridge that Gideon and Chandra blew up.
Also lol @ the story bringing up Jace's newfound sexy muscles like three times.
The Immortal Sun is most likely a Mirari. Memnarch as the Mirari could keep planeswalkers from entering Mirrodin, it makes sense to me that a Mirari could also be misused to keep planewalkers from LEAVING.
What I don't get is why Karn made his probes so powerful. Why even do that?
It's probably growing pains as a planeswalker - he assumed that sending something powerful was needed to keep readings intact. It's also possible that they are tainted with the oil (if only slightly, not enough to self-replicate) and cause the probe to go haywire over time.
I wouldn't be surprised if the Mirari on Ixalan (if that is what it is) caused the Vampires entirely.