My only guess is Euron Greyjoy will use the horn Dragonbinder to control one or more of Dani’s dragons. You know, the only plot device capable of removing Dani’s OP advantage because...drama. No one really cares about the fight for King’s Landing. We just want the Night King to get move on down south.
I’m still wondering how the Lannister’s are paying and feeding their troops. They ran out of gold seasons ago and the best farmlands have revolted.
I'm surprised the Iron Bank of Braavos hasn't made an appearance recently. I would think that the Bank might be a powerful adversary to the Lannisters/a powerful friend to Danaerys. They want to get paid.
” the only plot device capable of removing Dani’s OP advantage”
Also if a dragon gets killed beyond the wall it could be resurrected into the dead.