Eternal Scourge + Young Deathclaws + Crystalline Crawler + Altar of Dementia + The Earth Crystal

Eternal Scourge

Young Deathclaws

Crystalline Crawler

Altar of Dementia

The Earth Crystal

How it works

1. Activate Eternal Scourge's scavenge ability, granted to it by Young Deathclaws, by paying 3 and exiling Eternal Scourge from your graveyard, putting six +1/+1 counters on Crystalline Crawler due to The Earth Crystal.
2. Activate Crystalline Crawler six times by removing six +1/+1 counters from it, adding 6.
3. Cast Eternal Scourge from exile by paying 3.
4. Activate Altar of Dementia by sacrificing Eternal Scourge.
5. Repeat.

This clever loop relies on Young Deathclaws to grant Eternal Scourge scavenge while it sits in your graveyard, allowing you to continually exile it to pump Crystalline Crawler. Because The Earth Crystal doubles any +1/+1 counters placed on your creatures, that single scavenge activation drops a massive six counters onto the Crawler, which you can immediately strip away for six mana of any color. That floating mana easily covers the cost to recast Eternal Scourge from exile, and once it's back on the battlefield, Altar of Dementia lets you sacrifice it right back to the graveyard to mill your opponents while fueling the engine all over again.