The Frost Knight Horse Gear (Mythical Arduanatt: Pure White) alters the graphics of the relevant mythical horse incorrectly:

Note the black legs, gold lines on legs,  black smoke effect, and dark reddish feathers around the hooves.  This is identical to how Mythical Arduanatt's first form, Red, looks with the Solar Knight Horse Gear:

When Pure White Mythical Arduanatt is supposed to look like this: