Proceed at your own risk.
Stompy was the nickname given to the kaiju by Eeebs that fought during The Battle of Villagetown. Stompy was summoned using a Wish (item). It is noting that when a monster or being is summoned, they are left disoriented by Summoning Sickness, as shown with Stompy after it was summoned. It is also worth noting that the hide of a kaiju is very valuable as Nelmi had inferred during The Battle of Villagetown.
It fought in the Halls of Agemmon against the final guardian, a Red Wyrm. Like most summonings, it returned to its home dimension after the battle. As a Kaiju, Stompy is a Greater Being, that of which can only be found in the 15th dimension and above.
Stompy was not referenced after NK6, he may be trapped underground until he can get dug out. Request assistance may also despawn the mob after use, no one is sure.