Your opponent says, Go to attacks, you nod, and they tap the Baloth to indicate its attacking.So, lets say your opponent attacks with a [4] Soraya the Falconers banding ability to create a band of Soraya and a Watchwolf.You must announce that youre using Banding after your opponent declares attackers, but before blockers are declared
All of these questions should factor into your decision, and luckily youre not alone in trying to figure all that out
Typically the trend has been: the worse your matchup against the graveyard decks are, the more likely you are to have high-impact answers like Leyline of the Void
At least, you should with a card that has such high combo potential
Also, the player can sacrifice The Witch's Vanity itself for a Bargain effect if they can't afford to or don't want to wait for The Witch's Vanity to make Bargain fodder with Chapters II and III
Thats just good