Duke Ulder Ravengard, and Éomer, Marshal of Rohan

Prerequisites

• Duke Ulder Ravengard on the battlefield
• Éomer, Marshal of Rohan on the battlefield
• Éomer cannot be blocked and killed by an opponent
• You have at least two opponents

Steps

1. At the beginning of combat, Duke Ulder Ravengard triggers, giving Éomer an additional instance of myriad until end of turn
2. Declare Éomer as an attacker
3. Each instance of Éomer's myriad ability triggers, creating at least one token copy of it tapped and attacking each other opponent
4. Put all Éomer tokens into your graveyard due to the legend rule
5. When the Éomer token(s) die, each other Éomer triggers, untapping all creatures you control and causing you to get at least one additional combat phase after this one
6. Repeat from step 2 each combat phase
7. Once you have an arbitrarily high number of combat phases, you may have Duke Ulder Ravengard give myriad to any other creatures you control

Results

• Infinite combat phases
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite mana creatures you control can produce
• Infinite untap of creatures you control