During your Main Phase: You can Set 1 "World Legacy" Spell/Trap from your Deck, but it cannot be activated this turn while you have no "World Legacy" monster in your GY
It's reds way of card advantage which is almost always weaker then just having extra cards in hand
Fate Unraveler, Underworld Dreams, Razorkin Needlehead, and Kederekt Parasite are all very similar, and theyre often seen in the same decks together
X were retired at the end of the Platinum era of the Trading Card Game, to be replaced in HeartGold & SoulSilver by both Pokmon Prime and Pokmon LEGEND
40 to 50% of your deck transfers between starter decks when upgrading
The blog post hints at further progress in its closing remark: There's much more work to be done as we continue to make our games, communities, and company more inclusive. Ive reached out to Wizards of the Coast to see if a spokesperson can clarify further.