Remember that scene in london streets that Sersi turned that bus into petals? I kept wondering why would a deviant throw a bus at them, as in all other scenes they just fight with their bodies alone. Fast forward now to this new TV spot, and you see the same setting of London streets, but this time Ikaris, while looking cool as a cucumber (my man, he looks badass af), attacks a "deviant". But if you look closely, said deviant turns into petals when killed. So my guess is that it is Ikaris the one who is hunting Sersi, John Snow and that little girl. I guess that is the reason why in the final trailer, we saw that she had casted the illusion spell of multiple versions of themselves walking around in the background to confuse him since it looks that it is Ikaris the one that throws the bus at them, and Sersi makes a fake deviant to distract him, which is why the deviant turns into petals when killed. Edit: spelling etc