Since at least the days of Weatherlight, seeing an opponent dumping creatures into his graveyard en masse is reasonable cause for alarm. Most likely, you have to worry about some or all of those creatures being brought into play, often circumventing their mana costs along the way. But what happens if reanimation isn't the plan? What if the graveyard is exactly where they're intended to stay, and you in fact have to worry about something more fearsome than any or all of the creatures there... because it's in fact all of them at once?
