Lethal Vapors, Encroaching Mycosynth, and Null Rod

Prerequisites

• Lethal Vapors on the battlefield
• Encroaching Mycosynth on the battlefield
• Null Rod on the battlefield

Steps

1. Whenever a creature enters the battlefield, Lethal Vapors triggers, destroying that creature
2. Because Null Rod 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