Whoa, this is really cool. First off, I'm super happy that sagas are back. They fit perfectly in Theros. Second, this card does so many cool things. You have a lot of flexibility with the stolen creature, and chapter III after chapter II is pretty brutal.

I like Sagas, glad they can come back.

I like Sagas, but I'm not happy to see them outside of Dominaria. Sagas were a huge part of Dominaria's new "history plane" identity that took them about a decade to figure out, and now they're just casually giving them to Theros? I was hoping they'd try to preserve Saga design space for our next tip to Dominaria (instead of making them a decidious mechanic, or whatever is going on here). Besides, the point of the Sagas in Dominaria was that they all depicted events or pieces of lore that we had a first-hand familiarity with. I don't think you can do that sort of thing with Theros, unless you're just ripping off Greek mythology 1:1 and just slightly changing the name (e.g. Akros instead of Troy), resulting in exactly the paint-by-numbers worldbuilding people criticised about original Theros block.

I see what you're getting at, but have a bit of delta. I think Theros, in particular, is a natural fit for Sagas as well as Dominaria. A big part of it is that Theros's mechanical identity is "Enchantments!", at which point, hey, sagas are an enchantment type. The other part is that 1:1 ripoff. A lot of people had trouble with it, but it also clearly worked for the masses enough that we've seen the same treatment in Eldraine. I guess it really started with Innistrad's nods to horror classics, the difference being that Innistrad at least had more to it than that (Eldraine too, to a lesser extent. More than Theros at least.) If those two points are both in place, Sagas are a natural result.

I feel like you'd argue with the second point being a good thing, and I sustain that objection, but it's fairly clearly there for better or worse.

(I'd also love to see things branch out from their origins more. Like, we could get the shocklands WITHOUT Ravnica. The names were generic for that very reason. So why don't we?)

I think it's a mistake to not reuse great mechanics when possible.