Stampede

Stampede (スタンピード) is the term where a group of monsters on a rampage.

Description
Monsters possessed by the urge to destroy form a swarm and become a storm of disaster that engulfs everything. It is said to be a precursor to the resurrection of the Demon Lord, the coming of the end times, etc, but the cause is unknown. What it is known is that once a stampede occurs, it can cause tremendous damage.