Leonardo, Sewer Samurai + Solemnity + Shield Sphere + Phantom Train

Leonardo, Sewer Samurai

Solemnity

Shield Sphere

Phantom Train

How it works

1. Activate Phantom Train 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 loop relies on Leonardo, Sewer Samurai to turn your graveyard into a second hand for tiny creatures, letting you cast Shield Sphere for zero mana over and over again. The secret sauce that makes this sustainable is Solemnity, which acts as a protective shield for your board—it prevents Leonardo's finality counters from ever landing on the Sphere, while also nullifying the -0/-1 counters that would normally dismantle the Sphere when it blocks. With that friction removed, Phantom Train happily devours the repeatedly resurrected Shield Sphere as fuel, growing larger with infinite +1/+1 counters while generating endless sacrifice, ETB, and death triggers.