Yarok, the Desecrated + Fertilid + Crystalline Crawler + Avenger of Zendikar + Conspiracy

Yarok, the Desecrated

Fertilid

Crystalline Crawler

Avenger of Zendikar

Conspiracy

How it works

1. Activate Fertilid by paying 1 and removing a +1/+1 counter from it, causing you to search your library for a basic land card and put it onto the battlefield tapped.
2. When the land enters the battlefield, Avenger of Zendikar's second ability triggers twice, putting two +1/+1 counters on each creature you control.
3. Activate Crystalline Crawler's first ability twice by removing two +1/+1 counters from it, adding 1.
4. Repeat.

This fascinating engine relies on a clever interplay of triggered doubling and resource conversion to empty your library of basic lands. With Conspiracy naming Elementals or Plants (making Fertilid and Crystalline Crawler benefit from Avenger of Zendikar's landfall buffs), every land brought into play causes Avenger of Zendikar's landfall ability to trigger twice thanks to Yarok, the Desecrated's static doubling effect. The resulting +1/+1 counters placed on Crystalline Crawler and Fertilid can then be stripped away for mana and activation costs, fueling the next loop indefinitely.