Karn, Legacy Reforged, Lithoform Engine, Clock of Omens, Basalt Monolith, and Grim Monolith

Prerequisites

• Karn, Legacy Reforged on the battlefield
• Lithoform Engine on the battlefield
• Clock of Omens on the battlefield
• Basalt Monolith on the battlefield
• Grim Monolith on the battlefield
• You control at least five additional artifacts
• available

Steps

1. At the beginning of your upkeep, Karn triggers
2. Holding priority, activate Lithoform Engine's first ability by paying and tapping it, copying Karn's ability
3. Resolve the copy of Karn's ability, adding for each artifact you control that cannot be spent to cast nonartifact spells
4. Activate Clock of Omens by tapping Basalt Monolith and Grim Monolith, untapping Lithoform Engine
5. Activate Basalt Monolith's second ability by paying , untapping it
6. Activate Grim Monolith's second ability by paying , untapping it
7. Repeat from step 2

Results

• Infinite colorless mana that cannot be spent to cast nonartifact spells
• Infinite mana artifacts you control can produce
• Infinite untap of artifacts you control