Endbringer and Thornbite Staff on the battlefield.
Thornbite Staff attached to Endbringer.
Endbringer does not have summoning sickness.
You have a way to give Endbringer deathtouch.
Steps
Give Endbringer deathtouch, if needed.
Activate Endbringer's first ability by tapping it, dealing 1 damage to an opponent's creature and destroying it due to Endbringer's deathtouch.
When the creature dies, Endbringer triggers, untapping itself.
Repeat from step 2.
You may also repeat this loop whenever a creature enters the battlefield under an opponent's control if you have a way to give Endbringer deathtouch indefinitely.
Results
Destroy all creatures that enter the battlefield under an opponent's control.
Destroy any number of creatures opponents control.