Leonardo, Sewer Samurai + Solemnity + Shield Sphere + Yahenni, Undying Partisan

Leonardo, Sewer Samurai

Solemnity

Shield Sphere

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing Shield Sphere.
2. Cast Shield Sphere from your graveyard by paying 0. It will not enter with a finality counter on it due to Solemnity.
3. Repeat.

This clever loop turns Yahenni, Undying Partisan into an endless sacrifice engine by leaning on Leonardo, Sewer Samurai to repeatedly pull Shield Sphere right back out of your graveyard for zero mana. Normally, Leonardo would burden recurred creatures with a finality counter, but Solemnity steps in to completely shut down counters of any kind from ever being placed. That means Shield Sphere can bounce back and forth between the battlefield and the graveyard infinitely, safely ignoring both its own -0/-1 blocking drawback and Leonardo's exile restriction while triggering endless sacrifices for Yahenni.