Regrowth + Emeritus of Abundance // Regrowth + Pyromancer Ascension + Turnabout + Yahenni, Undying Partisan

Regrowth

Emeritus of Abundance // Regrowth

Pyromancer Ascension

Turnabout

Yahenni, Undying Partisan

How it works

1. Cast a copy of Regrowth from exile by paying 1, targeting any card besides the actual Regrowth.
2. Pyromancer's Ascension's first ability triggers, allowing you to put a quest counter on it.
3. Resolve the copy of Regrowth, returning that card from your graveyard to your hand.
4. Declare Emeritus of Abundance as an attacker.
5. When Emeritus of Abundance attacks, it triggers, becoming prepared.
6. During your second main phase, cast a copy of Regrowth by paying 1, targeting the actual Regrowth card.
7. Pyromancer Ascension's first ability triggers, allowing you to put a quest counter on it.
8. Resolve the copy of Regrowth, returning Regrowth from your graveyard to your hand.
9. Cast Turnabout by paying its mana cost.
10. Pyromancer Ascension's second ability triggers, copying Turnabout.
11. Resolve a copy of Turnabout, untapping lands you control.
12. Activate those lands by tapping them, adding mana.
13. Resolve the remaining copy of Turnabout, untapping lands you control.
14. Activate those lands by tapping them, adding mana.
15. Activate Yahenni by sacrificing Emeritus of Abundance, producing that card's result.
16. Cast the card Regrowth from your hand by paying 1, targeting Emeritus of Abundance.
17. Pyromancer Ascension's second ability triggers, copying Regrowth and allowing you to target Turnabout with the copy.
18. Resolve both copies of Regrowth, returning Emeritus of Abundance and Turnabout from your graveyard to your hand.
19. Cast Turnabout by paying its mana cost.
20. Pyromancer Ascension's second ability triggers, copying Turnabout.
21. Resolve a copy of Turnabout, untapping lands you control.
22. Activate those lands by tapping them, adding mana.
23. Resolve the remaining copy of Turnabout, untapping lands you control.
24. Activate those lands by tapping them, adding mana.
25. Cast Emeritus of Abundance by paying 2.
26. Cast a copy of Regrowth from exile by paying 1, targeting Turnabout.
27. Both of Pyromancer Ascension's abilities trigger.
28. In response, activate Yahenni by sacrificing Emeritus of Ideation, producing that card's result.
29. Resolve Pyromancer Ascension's first abiliity, putting a redundant quest counter on it if desired.
30. Resolve Pyromancer Ascension's second ability, copying Regrowth and targeting Emeritus of Abundance with the copy.
31. Repeat from step 18.

This intricate loop relies on Pyromancer Ascension acting as a double-edged engine, growing quest counters while duplicating your spells once fully charged to multiply your effects. By casting and recasting Regrowth, you continually pluck key cards like Turnabout back from the graveyard, allowing Turnabout's copied activations to repeatedly untap your lands for massive mana generation. Yahenni, Undying Partisan puts this vast mana and recursion to work by providing a reliable sacrifice outlet for Emeritus of Abundance, ensuring creatures cycle seamlessly through the graveyard to trigger death loops and fuel the engine indefinitely.