This loop relies on a brilliant bit of anti-synergy circumvention, turning finality counters into non-issues while turning a humble artifact into an engine of infinite resources. Shilgengar, Sire of Famine provides the graveyard recursion engine by letting you sacrifice a creature to make Blood tokens, and later cashing in six of those Blood tokens to bring your graveyard back. The catch is usually the finality counters that come with these recurred creatures, but Solemnity completely shuts that drawback down by preventing counters of any kind from being placed on your permanents. This allows Leonardo, Sewer Samurai to repeatedly let you cast Shield Sphere straight from the graveyard for free during your turn, since the 0-power wall qualifies for Leonardo's recursion clause. Each time you sacrifice Shield Sphere to Shilgengar, you generate Blood tokens and trigger all your death and sacrifice effects infinitely, fueling an endless cycle of value.