A/N: a new picture has surfaced, revealing the new threat as mentioned. An enormous quadrupedal creature with magma type features and it looks to stand a bit taller than godzilla.

Also, some more info on Godzilla: Aftershock:

"Continuing the story of 2014's Godzilla after the catastrophic events in San Francisco, the novel finds the big lizard threatened as a terrifying new foe rises from the depths of the earth, unleashing a series of devastating earthquakes and driven by an unstoppable primal instinct that will test Godzilla like never before. Introducing characters from Godzilla: King of the Monsters, the graphic novel delves further into the activities of cryptozoological agency Monarch."

So this is a new subterranean kaiju.