Fiendlash, and Guilty Conscience

Prerequisites

• Fiendlash on the battlefield
• Guilty Conscience on the battlefield
• An additional indestructible creature on the battlefield
• All permanents attached to that creature
• You have a way to deal damage to that creature

Steps

1. Deal damage to the indestructible creature
2. Fiendlash triggers, causing the creature to deal damage equal to the creature's power to target player or planeswalker
3. Guilty Conscience triggers, dealing that much damage to the creature
4. Repeat

Results

• Infinite damage