Holding priority, cast Dualcaster Mage by paying its mana cost.
When Dualcaster Mage enters, it triggers, copying Graceful Reprieve, with the copy targeting Dualcaster Mage.
Resolve the copy of Graceful Reprieve.
Holding priority, activate Altar of Dementia by sacrificing Dualcaster Mage.
When Dualcaster Mage dies, Graceful Reprieve triggers, returning Dualcaster Mage from your graveyard to the battlefield.
Repeat from step 3.
Resolve all Altar of Dementia abilities from step 5.
This looping masterpiece begins by leveraging Dualcaster Mage's clever entry trigger to copy Graceful Reprieve, establishing a self-sustaining safety net that continuously returns Dualcaster Mage to the battlefield whenever it leaves. By feeding this resilient wizard directly into Altar of Dementia, you transform the endless cycle of sacrifice and revival into a lethal wave of milling. Every single iteration triggers Graceful Reprieve anew while fueling Altar of Dementia's sacrifice demands, letting you grind through any opponent's library down to the very last card.