Dawnsire, Sunstar Dreadnought + Vigor + Crystalline Crawler + Hellkite Charger

Dawnsire, Sunstar Dreadnought

Vigor

Crystalline Crawler

Hellkite Charger

How it works

1. Declare Hellkite Charger as an attacker, triggering it and Dawnsire.
2. Resolve the Dawnsire trigger, attempting to deal 100 damage to Crystalline Crawler, which will result in 100 +1/+1 counters being placed on it instead due to Vigor.
3. Holding priority, activate Crystalline Crawler's first ability seven times by removing seven +1/+1 counters from it, adding 5.
4. Resolve the Hellkite Charger trigger, causing you to pay 5 to untap all attacking creatures you control and to get an additional combat phase after this one.
5. Repeat each combat phase.

This clever loop turns your own firepower inward by having Dawnsire, Sunstar Dreadnought blast Crystalline Crawler for massive damage, which Vigor happily intercepts to pile a mountain of +1/+1 counters onto the Crawler instead of destroying it. From there, you strip away just a handful of those newly minted counters using Crystalline Crawler's mana ability to fund the hefty attack tax demanded by Hellkite Charger. Because Hellkite Charger grants an extra combat phase and untaps everything in the process, you can simply declare your attackers again to restart the whole cycle, netting infinite combat phases and boundless mana along the way.