The delayed triggered ability created by chapters I and II triggers separately for each of the target creatures, even if, somehow, they end up dealing combat damage to the same player at the same time
This effect drops off at higher power levels where decks are more likely to win through a combo than a mass of creatures, but this can stop many combos, like Glint-Horn Buccaneer, anything with Kiki-Jiki, Mirror Breaker, and combos that loop cards like Pyrite Spellbomb or Moonglove Extract for infinite damage
Cards can be from a variety of sets or a single set (at the time of this listing a number of Double Masters lands just went into these packs!)
A spell you cast this way can be the target of a later spell you cast this way
But in this case there is literally one copy of that card in existence and a celebrity apparently worth over $50 million decided he wanted it: it's the definition of a one-off valuation