This loop relies on Isilu, Carrier of Twilight's passive ability to grant your nontoken creatures persist, letting Spiteful Squad continually return from the graveyard with a -1/-1 counter whenever Shilgengar, Sire of Famine sacrifices it to generate Blood tokens. Because Spiteful Squad enters with two +1/+1 counters that can jump to another creature upon its death, and because Eirdu, Carrier of Dawn makes your creature spells cheaper to cast with convoke while providing a way to pivot back and forth in the face of combat or mana needs, you can easily fuel Shilgengar's mass-reanimation ability. By cycling Spiteful Squad endlessly through the graveyard, you accumulate an infinite horde of Blood tokens, endless death and sacrifice triggers, and unbounded +1/+1 counters to overwhelm the opposition.