Phyrexian Altar + Dualcaster Mage + Black Sun's Twilight

Phyrexian Altar

Dualcaster Mage

Black Sun's Twilight

How it works

1. Cast Black Sun's Twilight by paying 5
2. Holding priority, cast Dualcaster Mage by paying its mana cost.
3. When Dualcaster Mage enters, it triggers, targeting Black Sun's Twilight.
4. Holding priority, activate Phyrexian Altar by sacrificing Dualcaster Mage.
5. Resolve the Dualcaster Mage trigger, copying Black Sun's Twilight
6. Resolve the Black Sun's Twilight copy, returning Dualcaster Mage from your graveyard to the battlefield.
7. Repeat from step 3.