Copy Enchantment + Mirrormade + Oblivion Ring + Altar of the Brood

Copy Enchantment

Mirrormade

Oblivion Ring

Altar of the Brood

How it works

1. Cast Mirrormade by paying 2.
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 Copy Enchantment by paying 2.
6. Copy Enchantment 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 Copy Enchantment'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 Copy Enchantment.
13. Copy Enchantment 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.

This elegant loop turns a pair of flexible clones into an endlessly repeating self-sustaining cycle. By having Mirrormade and Copy Enchantment continuously enter as copies of Oblivion Ring—which in turn exile each other in a perpetual game of tag—you trigger Altar of the Brood with every single iteration to grind your opponents' libraries down to nothing. Because you can choose to break the chain at any moment by simply pointing the entering clone at a different target, this clever sequence lets you cleanly mill out the entire table on demand.