This clever loop is orchestrated by Traveling Plague, which has a remarkable recursion trigger: whenever the creature it enchants leaves the battlefield, the Aura simply returns itself from the graveyard straight to the battlefield. To fuel this engine, you use Shilgengar, Sire of Famine to sacrifice the creature currently bearing the Plague, which triggers the Aura's return clause while also letting Shilgengar generate Blood tokens (or set up a massive graveyard return with its six-token ability). Meanwhile, Gremlin Tamer serves as your watchful observer, utilizing its *eerie* ability to churn out a fresh 1/1 red Gremlin token every single time Traveling Plague re-enters the battlefield. Because the newly created Gremlin makes an ideal target for Traveling Plague to attach to upon its return, you can continuously sacrifice that token to Shilgengar and repeat the cycle to generate an infinite supply of death triggers, sacrifices, and Blood tokens.