This loop creates an infinite sacrifice engine by exploiting a clever rules interaction between Melira, Sylvok Outcast and Wingrattle Scarecrow. Because Melira prevents -1/-1 counters from being placed on your creatures, every time you feed Wingrattle Scarecrow to Sarcatog's sacrifice ability, the Scarecrow's persist trigger returns it to the battlefield completely free of its usual drawback. This allows you to sacrifice the Scarecrow an unlimited number of times to endlessly pump Sarcatog's power and toughness while triggering any other death, entry, or leave-the-battlefield effects you might need.