This brilliant little loop is fueled by Crookshank Kobolds, whose zero-mana cost lets you cast it repeatedly right out of your graveyard using the graveyard-casting permission granted by Leonardo, Sewer Samurai. While Leonardo normally saddles such recurred creatures with a finality counter upon entry, Solemnity completely shuts down counters of any kind, allowing the Kobolds to enter the battlefield clean time and time again. You simply sacrifice the Kobolds to Bartolomé del Presidio to start the engine, feeding Bartolomé endless +1/+1 counters while generating an infinite stream of sacrifice, death, and trigger events.