This clever recursion loop centers around Leonardo, Sewer Samurai, whose static ability lets you cast 1-power or 1-toughness creatures like Phyrexian Walker straight from your graveyard during your turn. Normally, those creatures would enter with a finality counter and be exiled upon dying, but Solemnity's static ability completely shuts down all counters from being placed on creatures. With that restriction nullified, you can use Bartolomé del Presidio to repeatedly sacrifice Phyrexian Walker for endless sacrifice, death, and trigger value while growing Bartolomé del Presidio into a massive threat.