Fiendlash, Donna Noble, and With Great Power...

Prerequisites

• Fiendlash on the battlefield
• Donna Noble on the battlefield
• With Great Power
• on the battlefield

Steps

1. Deal damage to Donna Noble
2. Donna Noble and Fiendlash trigger
3. Resolve the Donna Noble trigger, dealing damage to an applicable target
4. Resolve the Fiendlash trigger, targeting you, but dealing damage to Donna Noble instead due to With Great Power
5. Repeat from step 2

Results

• Infinite damage to target opponent