Toph, the First Metalbender, Bumi, Unleashed, and Thran Forge

Prerequisites

• Toph, the First Metalbender on the battlefield
• Bumi, Unleashed on the battlefield
• Thran Forge on the battlefield
• available

Steps

1. Cause Bumi to become an artifact using Thran Forge
2. Deal combat damage to an opponent
3. Bumi triggers, untapping all lands you control, including Bumi as it's a land due to Toph, and causing you to get an additional combat phase after this one
4. Repeat step 2 each combat phase

Results

• Infinite combat phases
• Infinite mana lands you control can produce
• Infinite untap of lands you control
• Infinite combat damage