Enduring Renewal + Phyrexian Altar + Reef Worm

Steps

1. Activate Phyrexian Altar by sacrificing Reef Worm, adding {U}.
2. When Reef Worm dies, it and Enduring Renewal triggers.
3. Resolve the Reef Worm trigger, creating a 3/3 Fish creature token.
4. Resolve the Enduring Renewal trigger, returning Reef Worm from your graveyard to your hand.
5. Activate Phyrexian Altar by sacrificing the Fish, adding {1}.
6. When the Fish dies, it triggers, creating a 6/6 Whale creature token.
7. Activate Phyrexian Altar by sacrificing the Whale, adding {1}.
8. When the Whale dies, it triggers, creating a 9/9 Kraken creature token.
9. Activate Phyrexian Altar by sacrificing the Kraken, adding {1}.
10. Cast Reef Worm by paying {3}{U}.
11. Repeat.