Lethal Vapors, Encroaching Mycosynth, and Damping Matrix

Prerequisites

• Lethal Vapors on the battlefield
• Encroaching Mycosynth on the battlefield
• Damping Matrix on the battlefield

Steps

1. Whenever a creature enters the battlefield, Lethal Vapors triggers, destroying that creature
2. Because Damping Matrix prevents Lethal Vapors's activated ability from being activated, it cannot be destroyed due to its ability

Results

• Destroy all creatures that enter the battlefield