Eternal Scourge + Young Deathclaws + Crystalline Crawler + Viscera Seer + Branching Evolution

Eternal Scourge

Young Deathclaws

Crystalline Crawler

Viscera Seer

Branching Evolution

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 Branching Evolution.
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 Viscera Seer by sacrificing Eternal Scourge.
5. Repeat.

This clever loop starts by using Young Deathclaws to grant Eternal Scourge scavenge, letting you exile it from the graveyard to target Crystalline Crawler. Because Branching Evolution doubles the incoming counters, that single scavenge pumps six +1/+1 counters onto Crystalline Crawler, which you can then remove to generate six mana of any color. That surplus mana easily pays to recast Eternal Scourge from exile, and while you're at it, Viscera Seer lets you sacrifice the Scourge to sculpt your draws between iterations. Since Eternal Scourge just returns to exile when targeted by opponents or goes back to the graveyard to be scavenged anew, you have a self-sustaining engine of endless sacrifices, triggers, and scries.