This brilliant loop relies on the interaction between Viscera Seer and the incredible staying power provided by Isilu, Carrier of Twilight (the back face of Eirdu, Carrier of Dawn), which grants each other nontoken creature you control persist. When you sacrifice Hulk, Strongest There Is to Viscera Seer, its new persist ability triggers to bring it right back to the battlefield—and because Hulk enters with its own +1/+1 counter from its static text, that counter immediately cancels out the -1/+1 counter from persist via state-based actions. This leaves Hulk completely clean and ready to be fed back into Viscera Seer all over again for an endless chain of sacrifices, enter-the-battlefield triggers, and scrys.