The thunder horse in seen in the secret saturdays Beasts of the fifth sun. In the ice cavern level, Zak has to ride the thunder horse overtop the icicles. The thunder horse is a large, grayish, and dotted equine. This huge cryptid's hoofbeats were said to be the origin of thunder. It is actually related to ancestors of either large hores, or large rhinos. This creature's indestructable hooves allow it run over spiked surfaces. This creature is also known for killing bison as a self defense. The early indians of central-north America were shocked at the immense size of this beast.