How do you do an earthquake on war of the monsters?

you only can do this if you have another controller. so pick you monster and you opponent. then you pick baytown. pick one of the monsters, because one has to stand around. so you have to destroy all the billboards first. then you destroy all the buildings. after you destroy all the buildings, a earthquake will come down, and will make a abyss on the streets. it won't work, if 2 monsters destroy all the billboards and buildings.

PS. i tryed it a couple of times, it's awesome.