The Sibsig Ceremony + Myr Retriever + Workshop Assistant + Heartless Summoning

The Sibsig Ceremony

Myr Retriever

Workshop Assistant

Heartless Summoning

How it works

1. Cast Workshop Assistant by paying 0.
2. When Workshop Assistant enters the battlefield, The Sibsig Ceremony triggers, destroying Workshop Assistant and creating a 2/2 Zombie Druid creature token.
3. When Workshop Assistant dies, it triggers, returning Myr Retriever from your graveyard to your hand.
4. Cast Myr Retriever by paying 0.
5. Myr Retriever enters and dies as a state-based action due to having 0 toughness.
6. When Myr Retriever dies, it triggers, returning Workshop Assistant from your graveyard to your hand.
7. Repeat.