Phyrexian Altar + Dualcaster Mage + Lively Dirge

Prerequisites

There's a creature card in your graveyard with mana value 4 or less.

Steps

1. Cast Lively Dirge by paying {1}{B} plus an additional {2} to select its second mode, targeting a card in your graveyard.
2. Holding priority, cast Dualcaster Mage by paying its mana cost.
3. When Dualcaster Mage enters, it triggers, targeting Lively Dirge.
4. Holding priority, activate Phyrexian Altar by sacrificing Dualcaster Mage.
5. Resolve the Dualcaster Mage trigger, copying Lively Dirge
6. Resolve the Lively Dirge copy, returning Dualcaster Mage from your graveyard to the battlefield.
7. Repeat from step 3.