Mirrormade, Estrid's Invocation, Oblivion Ring, and Altar of the Brood

Prerequisites

• Mirrormade in hand
• Estrid's Invocation in hand
• Oblivion Ring on the battlefield
• Altar of the Brood on the battlefield
• available

Steps

1. Cast Mirrormade by paying
2. Mirrormade enters the battlefield as a copy of Oblivion Ring, triggering Altar of the Brood and itself
3. Resolve the Altar of Brood trigger, causing each opponent to mill a card
4. Resolve the Mirrormade's trigger, exiling Oblivion Ring
5. Cast Estrid's Invocation by paying
6. Estrid's Invocation enters the battlefield as a copy of the Oblivion Ring copy, triggering Altar of the Brood and itself
7. Resolve the Altar of Brood trigger, causing each opponent to mill a card
8. Resolve the Estrid's Invocation's trigger, exiling Mirrormade
9. Mirrormade leaves the battlefield, triggering itself, returning Oblivion Ring from exile to the battlefield
10. Altar of the Brood and Oblivion Ring trigger
11. Resolve the Altar of Brood trigger, causing each opponent to mill a card
12. Resolve the Oblivion Ring trigger, exiling Estrid's Invocation
13. Estrid's Invocation leaves the battlefield, returning Mirrormade from exile to the battlefield
14. Repeat from step 2 until each opponent has an empty library, then end the loop by choosing to copy or exile any other permanent

Results

• Infinite mill