Officially, the set includes 172 cards - not including those featured as part of the Trainer Gallery subset, of which there are 30 - but there is also an additional collection of Secret Rare items to keep an eye out for
Rebecca was the OP-04 Queen and, with OP-05, she gained so many good cards
If you put this on a good non-legendary creature while an opponent controls their commander, you force them to sacrifice one to the legend rule
If all targets for such a spell have become illegal by the time that spell tries to resolve, the spell won't resolve and none of its effects will happen
Of course, the rest of the card is nasty too: Its as close as well get to Grave Pact in the command zone
That's not cool, and it's not something I want to be doing, so I try to have a range of decks to play on any given day