Preston, the Vanisher + Delney, Streetwise Lookout + Sefris of the Hidden Ways + Altar of Dementia + Rilsa Rael, Kingpin

Preston, the Vanisher

Delney, Streetwise Lookout

Sefris of the Hidden Ways

Altar of Dementia

Rilsa Rael, Kingpin

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 Rilsa Rael from your graveyard onto the battlefield.
5. When Rilsa Rael enters, it and Preston trigger twice due to Delney.
6. Holding priority, activate Altar of Dementia by sacrificing Rilsa Rael.
7. Resolve a Preston trigger, creating a token copy of Rilsa Rael that is a 0/1 Illusion.
8. When the Rilsa Rael token enters, it triggers twice due to Delney.
9. Resolve the Rilsa Rael token triggers, venturing into Undercity twice.
10. Resolve the second Preston trigger from step 5, creating a token copy of Rilsa Rael that is a 0/1 Illusion.
11. Repeat steps 8 and 9 one additional time.
12. Resolve the first Rilsa Rael trigger from step 5, venturing into Undercity and completing Undercity.
13. Repeat from step 2.

This intricate loop turns the graveyard into an endless engine for dungeon crawling by leveraging Sefris of the Hidden Ways to recur creatures. Delney, Streetwise Lookout acts as a crucial multiplier, doubling Sefris's completion ability and Preston, the Vanisher's Illusion-copy triggers whenever a low-power creature like Rilsa Rael, Kingpin enters the battlefield uncast. As you sacrifice Rilsa Rael to Altar of Dementia and let Preston recreate her token copies, Delney ensures those enter-the-battlefield triggers accelerate your progress through the Undercity at astonishing speeds.