As far as I knew at the time, there wasnt a cartoon, show, video game, comic book or any kind of media that expands on the story of Streets of New Capenna
You can sacrifice a good number of lands and then search for Field of the Dead as part of its effect
(It is a huge mystery, but Deoxys, Yveltal or Primal Groudon/Kyogre are also suspects for causing it)
Its a nice way to slow an opponent down, but it has little use as far as actually securing victory goes
While Mega Absol ex does have high HP as a Mega Evolution Pokemon, it's not as bulky compared to most other Mega Evolutions
The two pairs of rare Meld cards, given how powerful they are on their own, will also be worth trying, with Gisela in particular having a similar set of hyper-efficient stats to the much loved (and hated) Baneslayer Angel from the Standard of the past