Voltaic Key, Forsaken Monument, Rings of Brighthearth, and Thran Dynamo

Prerequisites

• Voltaic Key on the battlefield
• Forsaken Monument on the battlefield
• Rings of Brighthearth on the battlefield
• Thran Dynamo on the battlefield

Steps

1. Activate Thran Dynamo by tapping it, adding
2. Forsaken Monument triggers, adding
3. Activate Voltaic Key by paying and tapping it, targeting itself
4. Rings of Brighthearth triggers, causing you to pay to copy Voltaic Key's ability, targeting Thran Dynamo
5. Resolve both Voltaic Key abilities, untapping it and Thran Dynamo
6. Repeat

Results

• Infinite untap of all artifacts you control