Everything that you have killed over the years in video games have now joined a super-alliance to destroy the Earth. This includes bosses as well.
This includes everything from the tiny 8-bit sprites to the colossal Reaper Destroyers.
How screwed is Earth?
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Reapers, The flood, the covenant, the didact, darth everybody, the mahjarrat, sauron, sauruman, the droids, GLaDoS, the taliban, the russians, the chinese, general unnamed terrorists, zombies (oh so many zombies), more zombies, and a bunch of other stuff i forget. Yeah we're -blam!-ed.