Leonardo, Sewer Samurai + Solemnity + Extruder + Phyrexian Walker

Leonardo, Sewer Samurai

Solemnity

Extruder

Phyrexian Walker

How it works

1. Activate Extruder by sacrificing Phyrexian Walker.
2. Cast Phyrexian Walker from your graveyard by paying 0. It will not enter with a finality counter on it due to Solemnity.
3. Repeat.

This loop cleverly exploits a protection clause to bypass the usual cost of graveyard recursion: thanks to Solemnity, counters simply cannot be placed on your permanents. This allows Leonardo, Sewer Samurai to let you repeatedly cast Phyrexian Walker from your graveyard for zero mana without saddling it with a finality counter. Meanwhile, Extruder provides the sacrifice outlet to send the Walker right back to the graveyard while fueling your other threats with endless +1/+1 counters.