Old piebald rounsey
The old piebald rounsey is a swaybacked, broken-down stot that is ridden by Podrick Payne.
Where Pod acquired the horse is not known, but presumably as it is such pitiable quality he was able to make it his own as nobody else wanted it. Its coat is a piebald pattern.
The piebald rounsey’s constitution must be much better than its appearance as the horse serves Pod well enough. He rides it throughout his travels with Brienne of Tarth across all sorts of terrain and it does not break down or go lame and can keep up with Brienne’s bay mare, which was given to her by Jaime Lannister.
A Feast for Crows
At the beginning of her quest to find Sansa Stark, in the queue to enter Duskendale, Brienne of Tarth glances behind her and notices a skinny boy on a piebald rounsey further back. Later the hedge knight Ser Creighton Longbough mentions seeing some farm boy on a piebald horse go by while he was on watch.
Going about her business Brienne keeps catching glimpses of the skinny boy on the piebald rounsey. She realizes that the boy is following her and confronts him by sneaking up and giving the old horse a whack across the rump with the flat of her longsword, causing the horse to rear and the boy to fall off. The boy turns out to be Tyrion Lannister’s former squire, Podrick Payne.
– Ser Hyle Hunt, talking about Podrick Payne’s mount
That rounsey may be the most hideous horse I’ve ever seen.