Beast Spirit of Thunder
The Beast Spirit of Thunder was created from Ancient Beatmon of the Warrior Ten. It was hidden in the ocean. A Whamon accidentally swallowed it then got stuck in a cave. As quiescent would have it the Legendary Chosen happened to save a battle against Grottomon in this cave. Whamon tried to help by shooting Grottomon with water from his spout and released the Beast Spirit of Thunder at the same time. Shibayama Junpei then took it and used it to spirit evolve into Bolgmon.
(Note: Is called Spirit of Thunder B in the TCG.)