The Thirteenth Doctor + Crystalline Crawler + Gravecrawler + Ashnod's Altar

The Thirteenth Doctor

Crystalline Crawler

Gravecrawler

Ashnod's Altar

How it works

1. Activate Ashnod's Altar by sacrificing Gravecrawler, adding CC.
2. Cast Gravecrawler from your graveyard by paying .
3. The Thirteenth Doctor's first ability triggers, putting a +1/+1 counter on Crystalline Crawler.
4. Activate Crystalline Crawler's first ability by removing a +1/+1 counter from it, adding .
5. Repeat.

This clever loop transforms Ashnod's Altar and Gravecrawler into an engine for infinite sacrifice by utilizing Gravecrawler's ability to be repeatedly cast from the graveyard as long as you control another Zombie. To fuel that recursion endlessly, Crystalline Crawler steps in: whenever The Thirteenth Doctor triggers from casting Gravecrawler outside your hand, it places a +1/+1 counter on Crystalline Crawler, which can then be immediately converted into the necessary black mana by removing that counter. Meanwhile, Team TARDIS sits on the board waiting to untap your creatures during the end step if things stall out, though this active loop already generates endless death triggers, enters-the-battlefield events, and colorless mana on the spot.