Quandrix Command + Crystalline Crawler + Dualcaster Mage + Lae'zel, Vlaakith's Champion

Quandrix Command

Crystalline Crawler

Dualcaster Mage

Lae'zel, Vlaakith's Champion

How it works

1. Cast Quandrix Command by paying its mana cost, choosing its first and third modes.
2. Holding priority, cast Dualcaster Mage by paying its mana cost.
3. When Dualcaster Mage enters, it triggers, copying Quandrix Command, with the copy's first mode targeting Dualcaster Mage and the copy's third mode targeting Crystalline Crawler.
4. Resolve the copy of Quandrix Command, returning Dualcaster Mage from the battlefield to your hand and putting three +1/+1 counters on Crystalline Crawler due to Lae'zel.
5. Holding priority, activate Crystalline Crawler three times by removing three +1/+1 counters from it, adding 1.
6. Repeat from step 2.

This intricate loop harnesses the self-replacing nature of Dualcaster Mage by using its entry trigger to copy Quandrix Command, whose first mode bounces the Mage right back to your hand so it can be cast again. Lae'zel, Vlaakith's Champion ensures that the Command's third mode turbocharges Crystalline Crawler by granting extra +1/+1 counters every time it resolves. You then cash in those newly minted counters using Crystalline Crawler's mana-producing ability to fully fund the next iteration of the spellcasting cycle.