Whole episode back-story for the horse. Or I fucking riot.
Titles.
Scene 1 - a kindly farmhand is helping to deliver a foal, both parents are grey horses but this one...white. "You'll do great things one day, I name you hope"
Scene 2 - farmhand is eviscerated by rampaging c***s of no determinate origin.
Scene 3 - Hope survives grazing on a hillside (10 minute montage)
Scene 4 - Hope pursued by earlier farmhand, now a white walker...
Honestly, this shit writes itself.