It can allow decks to pop-off quicker, which hopefully does the job of balancing the metagame, and not just walling out archetypes completely in the same way a card like Fury did in Modern (nuking mana dorks and other go-wide decks for no mana)
It is assembled over time, across sets, through trades, private sales, and the occasional find at pokemon card shows near me searches that lead you to a local event where someone has the exact promo you have been looking for
It does this with the help of cards such as Griffoh and Black Chaos the Ultimate Magical Swordsman to access Mind Shuffle, Mystical Celtic Sage and Skull Archfiend of Chaos to produce card advantage, and Black Chaos the Dark Chaos Magician and Black Luster Soldier Soldier of Light and Darkness to interact with the opponent
Jenna Pitcher is a freelance journalist writing for IGN
It will overwrite the old game but keep all of your decks