The Sibsig Ceremony + Myr Retriever + Junk Diver + Armor Wars

The Sibsig Ceremony

Myr Retriever

Junk Diver

Armor Wars

How it works

1. Cast Junk Diver by paying 0.
2. When Junk Diver enters the battlefield, The Sibsig Ceremony triggers, destroying Junk Diver and creating a 2/2 Zombie Druid creature token.
3. When Junk Diver dies, it triggers, returning Myr Retriever from your graveyard to your hand.
4. Cast Myr Retriever by paying 0.
5. When Myr Retriever enters the battlefield, The Sibsig Ceremony triggers, destroying Myr Retriever and creating a 2/2 Zombie Druid creature token.
6. When Myr Retriever dies, it triggers, returning Junk Diver from your graveyard to your hand.
7. Repeat.

This clever loop relies on The Sibsig Ceremony to drastically slash the cost of your creature spells while instantly sacrificing them upon entry to trigger their death abilities. As Junk Diver hits the battlefield and falls to the enchantment's wrath, its death trigger fishes Myr Retriever back out of your graveyard. You then deploy Myr Retriever, which suffers the exact same fate under The Sibsig Ceremony but rewards you by returning Junk Diver in return. While Armor Wars isn't strictly necessary for the core loop to spin infinitely, its second chapter can help grease the wheels by making artifact spells even cheaper, or its final chapter can eventually close out the game once you've built up your board.