MTG >Combos >Card with Free Sacrifice ability +Putrid Goblin +First Day of Class +

Cast First Day of Class Sacrifice Putrid Goblin Persist's ability will trigger, and Putrid Goblin will come back to the battlefield with a -1/-1 counter on it. First Day of Class's ability will trigger, adding a +1/+1 counter. +1/+1 and -1/-1 counters cancel each other out. Repeat the process for infinite ETB.