There is a little context as to how Karn went back in time, He was designed to be a Time Traveler Originally (hence why he is made of Silver, it is apparently immune to the damage from time travel) and he has traveled back through time before, so he has experience with it so going through a "Time Rift" to a specific spot in time isn't a huge leap for him to do.
Doesn't make much sense still though, but..well Time magic in MTG is strange anyways. *looks at Sarkhan*
Given that the Praetors hated Tezzeret going there would be utterly insane on his part
Him going back with Elesh Norn in charge is a good way to get himself flayed.
That is your problem Bo1 is a terrible "grinding" format, as it lets the decks that are super strong game 1 run rampant. Imagine the Meta that Dredge would invoke if Vintage were Bo1s
Plot twist, Nicol tries to call Tezzeret to take the sun away so he can get away, The Bridge Opens up to Amonkhet..then Garruk shows up and axes Tezzeret from behind. Gives the thumbs up and leaves.
Then they imprison him somewhere..and we get Silence of the Bolas.
((God I hope they don't do that))
I imagine most of the Bolas planeswalkers will betray him once they find out what he is actually up to.
The plot fairy once again flew down to flick her magic wand and make the plot happen.
Because he is chilling on Amonkhet opening the Bridge because Bolas isn't stupid enough to Risk his only way to get Off the plane in direct battle?
You do realize that most of the major characters at this point are completely safe right? There hasn't been an actually important death in the series since Book 3.
Now now, I gotta defend this one. Pia going all revolution leader makes sense given that she saw her Husband/Daughter killed. That would happen in like every fiction story line ever. Even A song of Ice and Fire pulled the "Person we said was dead has really been alive the whole time and doing important things off screen." card with Griff and Griff Jr.
He is immune to Phyresis, that is how he could spy on them for Bolas in Scars.
Old Phyrexia was a threat because they had Planar Bridges, it was something we were introduced to when we were first introduced to them.
The Mirari was not remotely an inter-planar threat, it wasn't even a world ending threat. Karona was a Planetary Threat, However she wasn't actually created by The Mirari..she was created when Kamahl killed Phage/Akroma/Zangora all at once, in what was stupid moment, but Legions and Scourge are as bad as Agents of Artifice.
The Rifts were kind of Stupid, The ones because of the Explosion of Tolaria and Teferi's Phasing made sense, The Overlay spots had the problem of the Overlay not being localized like that, as the entire plane of Rath got overlaid and was the same size of Dominaria at the time of Overlay so all of Dominaria should have had a rift above it.
The Nicol Bolas one and the Karona one were dumb though, If Karona's creation made "The biggest" Rift..then where is the one from The first time it happened? And Planeswalker Slap fights happen all the time without tearing the fabric of space time, but Nicol Bolas vs Un-named Leviathan did?
Bolas himself is an Evil Planeswalker, that makes him an Inherent Planar Threat. However his Plan with the Eternals does make zero sense, and he lucked out with Tezzeret tripping over Rashmi randomly.
The Eldrazi are C'thulu Ripoff Spiders that live in the Blind Eternities, they are an Inherent Planar Threat.
New Phyrexia requires them to re-use the same one in a hundred trillion shot that happened with the Planar Bridge for Bolas, except it is even more of a stretch because it not only requires someone to invent a better Planar Bridge than Rashmi, it someone inventing it on that specific Plane. Nicol Bolas hitting the Lottery was a huge stretch, but hey the Multi-verse is a big place so I could let it slide.
Nicol Bolas AND the Phyrexians hitting that same Lottery, in Back to Back Storylines? No that is cheap.
Ixalan was really dark, Consider for a second.
A God Like Being going from plane to plane and imposing his personal will on peoples regardless of whether they like it or not just because he feels the need to do so.
Is that Bolas or Azor? Then the plan for Ixalan to use it as a fighting ground for a Planar Scale Brothers War, on that the people of the Plane have no choice in but will feel the effects of for centuries. Remember when Urza and Misrha showed up on Argoth and wrecked the entire place? Imagine that except for a whole world.
Then when Ugin failed to show up with Bolas, Azor set up 3 Xenophobic empires by playing Hot Potato with an artifact Containing the energies of a near god like being. Azor's actions set up what will likely be a very long war between 3 sets of not very good people, with the Brazen Coalition throwing people around.
Ixalan is a colorful place, but it is not a happy place to live.
I don't think it is going to do that much to standard, most planeswalkers are 4-6 casting cost, which means going full super friends jam is going to bork your mana curve, If it does anything we could see a "Toolbox" approach where we see 1 or 2 of several midrangey cards. Combined with the full Shock/Check mana bases if we are getting 36 planeswalkers it could lead to a standard where something like Mono Red splashes into another color go have a Rakdos Planeswalker that can finish the game out.
At least be honest about it instead of trying to hide it behind two paragraphs about "Darkness" because Shadows over Innistrad was not a good story line.