Thermopod + Dualcaster Mage + Ascend from Avernus

Thermopod

Dualcaster Mage

Ascend from Avernus

How it works

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

This engine spins up by casting Ascend from Avernus, laying the groundwork to mass-resurrect your graveyard once $X$ is high enough. You then interrupt it by casting Dualcaster Mage, whose entry trigger targets the original Ascend from Avernus to copy it. Before that copy resolves, Thermopod lets you sacrifice the Dualcaster Mage for red mana to keep your engine fueled. The resolving copy brings Dualcaster Mage right back from the graveyard, and because Thermopod also grants its creatures haste when needed (though here its sacrifice outlet is the real star), this loop can continually recur and sacrifice Dualcaster Mage to generate infinite mana, deaths, and triggers.