Leonardo, Sewer Samurai + Solemnity + Phyrexian Altar + Kobolds of Kher Keep

Leonardo, Sewer Samurai

Solemnity

Phyrexian Altar

Kobolds of Kher Keep

How it works

1. Activate Phyrexian Altar by sacrificing Kobolds of Kher Keep.
2. Cast Kobolds of Kher Keep from your graveyard by paying 0. It will not enter with a finality counter on it due to Solemnity.
3. Repeat.
4. Activate Phyrexian Altar by sacrificing the additional creature, adding one mana of any color.
5. Cast the creature from your graveyard by paying its mana cost. It will not enter with a finality counter on it due to Solemnity.
6. Repeat.

This loop turns the zero-mana cost of Kobolds of Kher Keep into an infinite mana and trigger engine, leveraging Leonardo, Sewer Samurai to repeatedly cast the creature straight from your graveyard. The crucial piece holding the entire mechanism together is Solemnity, which prevents finality counters from ever being placed on your creatures as they enter the battlefield, ensuring Leonardo's graveyard-casting restriction never locks you out. Finally, sacrificing the creature to Phyrexian Altar provides the mana needed to keep the cycle going or funds a win condition while generating infinite sacrifice and death triggers.