Yenna, Redtooth Regent + Airtight Alibi + Careful Cultivation + Phantatog

Yenna, Redtooth Regent

Airtight Alibi

Careful Cultivation

Phantatog

How it works

1. Activate Yenna by paying 2 and tapping it, creating a copy of Airtight Alibi attached to Yenna, and then untapping Yenna and causing you to scry 2.
2. When the Airtight Alibi token enters, it triggers. Holding priority, activate Yenna by tapping it, adding .
3. Resolve the Airtight Alibi trigger, untapping Yenna.
4. Activate Phantatog by sacrificing the Airtight Alibi token.
5. Repeat.

This elegant loop centers on Yenna, Redtooth Regent, whose ability to copy nonlegendary enchantments gets wonderfully out of hand when targeting Airtight Alibi, since the resulting token untaps Yenna as it enters. While the Airtight Alibi token's enter-the-battlefield trigger is still waiting on the stack, you can tap Yenna for green mana generated by Careful Cultivation attached to it (or use Yenna's own ability once it has reset), letting Phantatog step in to sacrifice the cloned Aura. Because Phantatog can devour the Airtight Alibi token for a pump, you clear the board to repeat Yenna, Redtooth Regent's copying process infinitely—pumping Phantatog to arbitrary size, securing infinite scry 2 triggers, and repeatedly triggering any "lifesgain" or enter-the-battlefield effects you have running.