Underworld Breach, Grinding Station, and Mox Amber

Prerequisites

• Underworld Breach on the battlefield
• Grinding Station on the battlefield
• Mox Amber on the battlefield

Steps

1. Activate Mox Amber by tapping it, adding one mana of any color among legendary creatures and/or planeswalkers you control
2. Activate Grinding Station by tapping it and sacrificing Mox Amber, causing yourself to mill three cards
3. Cast Mox Amber from your graveyard for its escape cost by exiling three cards from your graveyard
4. When Mox Amber enters the battlefield, Grinding Station triggers, untapping Grinding Station
5. Repeat

Results

• Infinite self-mill
• Near-infinite storm count
• Near-infinite mana among colors of legendary creatures and planeswalkers you control