I have issue with the walkers having a dragon. It flies in the face of what we've learned about dragons over the last 7 seasons.
why? because the Night King is not a Targaryen? if thats your reasoning, keep this in mind
the Targaryens want people to believe that they are a special type of human because it helps them maintain control. and most of the Targaryens themselves buy into that lie. but the concept of Targaryen Exceptionalism is bullshit
as an example, there are Targaryens that believe they are not at risk to the same diseases as regular humans. but during the Great Spring Sickness of the past, they died just like other humans.
some hardcore fans (most actually) do not agree with me, but they are clueless. they try to say "then how come Targaryens are the only people to bond dragons!?!" the reason is simple. they were the only people with dragon eggs.
in the past, some dragon eggs went missing and the Targaryen king at the time was paranoid. at face value, he didnt want someone over in Essos with Valyrian bloodline to bond a dragon and oppose them. but a bigger problem for him would have been if a non-Valyrian got one of those eggs and bonded a dragon. if that had happened, then people would have stopped looking at Targaryens as demigods
ill also say that there are non-Targaryens that have ridden dragons in the past. and instead of taking it as proof that Targaryens are not special, fans have convinced themselves "that person must have valyrian blood!"