Preston, the Vanisher + Delney, Streetwise Lookout + Sefris of the Hidden Ways + Yahenni, Undying Partisan + Underdark Explorer

Preston, the Vanisher

Delney, Streetwise Lookout

Sefris of the Hidden Ways

Yahenni, Undying Partisan

Underdark Explorer

How it works

1. Complete a dungeon.
2. Sefris' second ability triggers twice due to Delney.
3. Resolve the first trigger, returning up to one other creature from your graveyard to the battlefield.
4. Resolve the second trigger, returning Underdark Explorer from your graveyard onto the battlefield.
5. When Underdark Explorer enters, it triggers once and Preston triggers twice due to Delney.
6. Holding priority, activate Yahenni by sacrificing Underdark Explorer.
7. Resolve a Preston trigger, creating a token copy of Underdark Explorer that is a 0/1 Illusion.
8. When the Underdark Explorer token enters, it triggers twice due to Delney.
9. Resolve the Underdark Explorer token triggers, venturing into Undercity twice.
10. Resolve the second Preston trigger from step 5, creating a token copy of Underdark Explorer that is a 0/1 Illusion.
11. Repeat steps 8 and 9 one additional time.
12. Resolve the Underdark Explorer trigger from step 5, venturing into Undercity and completing Undercity.
13. Repeat from step 2.

This intricate loop turns the dungeon-delving mastery of Sefris of the Hidden Ways into a relentless engine for infinite progression. Thanks to Delney, Streetwise Lookout doubling the triggers of your low-power creatures, completing a dungeon allows Sefris to pull Underdark Explorer back from the grave alongside another creature. As Underdark Explorer enters the battlefield to seize the initiative, Preston, the Vanisher responds to the uncast creature by minting a 0/1 Illusion copy of it. By sacrificing the original Underdark Explorer to Yahenni, Undying Partisan in response, you clear the way for Preston's triggers to spawn even more copies, driving the party through the Undercity repeatedly to generate infinite resources, mana, and card draw.