wow...this new Horde mode is making this challenge unbelievably long. I was at 2b out of 5b damage done in zone 1 before the sudden alteration of the Horde and now two days later, I've barely gained 100m damage. Previously it took me about a day, to a day and a half to get 1b damage, now it's been over 48 hours with a meager 100m...rough....