I took a look back at rockfuff's video that we found.
The first thing that flashes is at 0:08 saying "ROCKRUFF". It is shown for 4 frames in total.
At 0:56 it says "#86", also for 4 frames.
Aliria said that #86 might be in reference to this hoard, so maybe it was the cat with short legs, but Rockruff denied the short leg cat. This leads me to believe that if there's another short cat that it will be Rockruff's. The horse could also have something else in common with the cat. Purple is in the color pallet this year so maybe the cat is purple and white with hints of black. The horse has stars surrounding it so maybe the cat's adult stage will be surrounded by stars or something else!