Six + Phyrexian Altar + Circle of the Land Druid + Skeleton Crew

Six

Phyrexian Altar

Circle of the Land Druid

Skeleton Crew

How it works

1. Cast Circle of the Land Druid from your graveyard for its retrace cost by paying 1 and discarding a land card.
2. Skeleton Crew triggers, creating a creature token.
3. When Circle of the Land Druid enters the battlefield, its first ability triggers, causing you to mill four cards.
4. Activate Phyrexian Altar twice by sacrificing the creature token and Circle of the Land Druid, adding 1.
5. When Circle of the Land Druid dies, its second ability triggers, returning a land card from your graveyard to your hand.
6. Skeleton Crew triggers, creating a creature token.
7. Repeat.