Leonardo, Sewer Samurai + Solemnity + Phyrexian Altar + Crookshank Kobolds

Leonardo, Sewer Samurai

Solemnity

Phyrexian Altar

Crookshank Kobolds

How it works

1. Activate Phyrexian Altar by sacrificing Crookshank Kobolds.
2. Cast Crookshank Kobolds 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 free recursion into an infinite mana engine by exploiting a clever rules interaction. Because Solemnity prevents counters from being placed on creatures, Leonardo, Sewer Samurai's drawback of adding a finality counter to creatures cast from the graveyard is entirely bypassed. This allows you to repeatedly cast Crookshank Kobolds from your graveyard for zero mana, sacrifice it to Phyrexian Altar for any color of mana, and repeat the process endlessly.