Thanks for letting me know about this topic. :) Il just add my 2 cents on how this could be done. The giants in skyrim has a lot of similarities to a white walker from the series, it wouldnt require a lot of modification to begin from there to create a white walker, some remoddeling and new textures and perhaps add some human animations to him and resize to he could realistically fit on a horse. Of course you gotta have wights minions surrounding the white walker, number of wights id imagine 10-20, the npc's could be a combination of recently slain npc's and draugr's, would be really cool if you slayed a npc in a snowy area they would be added to a White Walker faction resurrected and obedient after a set time AD. Only way to avoid them becoming wights has to be a flame related spell, maybe a custom burn corpse spell just for this purpose. Also, wherever the white walkers goes, the weather gets worse, more snow etc. The white walkers also adds potencial of new weapons and armor, mainly Dragonglass weapons, that are made from dragonglass ( possibly aquired through dragon kills drops) If you wanna know more about dragonglass, let me know, i dont want to spoil too much about the series. I got a lot more ideas to be added, but they are deeply into the spoiler area of the show, so im gonna keep my mouth closed about that, im just gonna say adding something AA relevant would be really cool, but the tv show is far behind this. Comparison Picture of giant and white walker in spoiler. :)